Minerals

A: acanthite, actinolite, adamite, adelite, adularia (variety of orthoclase), aegirine, aenigmatite, agardite, ajoite, åkermanite, alabandite, alamosite, albite, alleghanyite, allophane, almandine, amazonite (variety of microcline), amblygonite, amphibole, analcime, andalusite, andesine, andradite, anglesite, anhydrite, ankerite, annite, anorthite, anorthoclase, anthophyllite, antigorite, apachite, apatite, aphthitalite, apophyllite, aquamarine (variety of beryl), aragonite, arseniosiderite, arsenopyrite, augite, aurichalcite, autunite, axinite, azurite
B: bariopharmacosiderite, baryte, bastnäsite bauxite, bayldonite, beryl, beudantite, biotite, bismuth, bismuthinite, bixbyite, böhmite, borax, bornite, boulangerite, bradleyite, braunite, brochantite, bromargyrite, bromellite, brucite, buddingtonite, burkeite, bustamite, bytownite (variety of anorthite)
C: calcite, caledonite, carminite, carpholite, cassiterite, cavansite, celadonite, celestine, celsian, cerussite, chabazite, chalcanthite, chalcedony, chalcocite, chalcophyllite, chalcopyrite, chlorargyrite, chlorite, chloritoid, chlorophoenicite, chondrodite, chromite, chrysoberyl, chrysocolla, chrysotile, cinnabar, cleavelandite (variety of albite), clinochlore (variety of chlorite), clinoclase, clinoenstatite, clinohedrite, clinohumite, clinoptilolite, clinozoisite, cobaltarthurite, coesite, colemanite, columbite, conichalcite, connellite, cookeite, copper, cordierite, corkite, cornubite, cornwallite, coronadite, corundum, covellite, crandallite, creaseyite, cristobalite, crocoite, cronstedtite, cryptomelane, cubanite, cummingtonite, cuprite, cyanotrichite, cymrite
D: dachiardite, danburite, datolite, dawsonite, descloizite, devilline, diaboleite, diamond, diaspore, diopside, dioptase, dolomite, duftite, dussertite
E: edenite, emerald (variety of beryl), enargite, englishite, enstatite, epidote, epistilbite, epsomite, erionite, erythrite, ettringite, eucryptite, evansite
F: faujasite, fayalite, feldspar, feldspathoid, ferberite, ferrierite, ferro-actinolite, ferro-anthophyllite, ferrosilite, fleischerite, fluorapatite, fluorite, forsterite, franklinite
G: gahnite, galaxite, galena, ganophyllite, garnet, garronite, gaylussite, gedrite, gehlenite, gibbsite, gilalite, gismondine, glauberite, glaucochroite, glaucophane, gmelinite, goethite, gold, gonnardite, gordonite, goshenite (variety of beryl), graphite, greenalite, grossular, grunerite, gypsum, gyrolite
H: halite, halloysite, hanksite, harmotome, hausmannite, hedenbergite, hedyphane, heliodor (variety of beryl), hematite, hemimorphite, hercynite, heulandite, hidalgoite, holdenite, hollandite, hornblende, hübnerite, humite, hyalophane (variety of microcline), hydrocerussite, hypersthene
I: illite (variety of muscovite), ilmenite, imogolite
J: jacobsite, jadeite, jarosite, johannsenite, junitoite
K: K-feldspar, kalsilite, kaolinite, kegelite, kernite, kinoite, kintoreite, kolbeckite, kolicite, kraisslite, kyanite
L: labradorite (variety of anorthite), lanarkite, laumontite, lavendulan, lawsonite, lead, leadhillite, lepidocrocite, lepidolite, leucite, leucophanite, lévyne, linarite, lindqvistite, liroconite, litharge, luddenite
M: macfallite, magnesioferrite, magnesite, magnetite, magnetoplumbite, magnussonite, malachite, manganhumite, manganite, manganosite, mansfieldite, marcasite, margarite, massicot, mawbyite, mazzite, melanotekite, melanterite, melilite, mendipite, merlinoite, merwinite, mesolite, metatorbernite, metavariscite, mica, microcline, millerite, millisite, mimetite, minium, mirabilite, mixite, molybdenite, monazite, montgomeryite, monticellite, montmorillonite, mordenite, mottramite, muscovite
N: nahcolite, namibite, natrite, natrolite, natron, neotocite, nepheline, nontronite, northupite
O: offretite, okenite, oligoclase, olivenite, olivine, omphacite, opal, orientite, orpiment, orthoclase, overite
P: papagoite, paracelsian, paragonite, pargasite, paulingite, parnauite, pectolite, periclase, perovskite, petalite, pharmacosiderite, phenakite, phillipsite, phlogopite, phoenicochroite, pirssonite, plagioclase feldspar, plancheite, platinum, plumboferrite, plumbogummite, pollucite, prehnite, proustite, pseudobrookite, psilomelane, pumpellyite, pyrargyrite, pyrite, pyrochlore, pyrochroite, pyrolusite, pyromorphite, pyrope, pyrophyllite, pyroxene, pyroxmangite, pyrrhotite
Q: quartz
R: ranciéite, realgar, red beryl (variety of beryl), rhodochrosite, rhodonite, richterite, riebeckite, romanèchite, roselite, rutile
S: sanidine, sapphirine, scapolite, schairerite, scheelite, schorl, scolecite, scorodite, searlesite, segnitite sellaite, sericite (variety of muscovite), serpentine, shattuckite, shortite, siderite, sillénite, sillimanite, silver, skutterudite, smithsonite, sodalite, spangolite, spessartine, sphalerite, spinel, spodumene, spurrite, staurolite, stephanite, stibnite, stilbite, stilpnomelane, stishovite, strashimirite, stringhamite, strontianite, sulphohalite, sulphur, svabite, swedenborgite, sylvanite, sylvite
T: talc, tantalite, taramellite, tennantite, tenorite, tephroite, tetrahedrite, thénardite, thermonatrite, thomsonite, tincalconite, titanite, tobermorite, topaz, torbernite, tourmaline, tremolite, tridymite, trona, turquoise, tychite, tyrolite
U: ulexite, uraninite, uvarovite
V: vanadinite, variscite, vermiculite, vesuvianite, vivianite
W: wairakite, wardite, wavellite, wickenburgite, willemite, witherite, wollastonite, wulfenite, wüstite
X: xonotlite
Z: zeolites, zincite, zircon, zoisite

Primary and Secondary Minerals

Minerals are primary when they form directly by crystallisation from molten magma, precipitation from magmatic fluids or sublimation from gases. They are secondary when they form from alteration of primary rocks, by weathering, metamorphic or hydrothermal processes. Whether they are primary or secondary is determined by their formation, not by their composition, and the same mineral species may occur sometimes as a primary mineral and sometimes as a secondary mineral.

The terms hypogene and supergene are closely associated with, but not synonymous with, primary and secondary. Hypogene processes are processes that occur deep within the earth, and supergene processes occur near the earth’s surface. Hypogene processes tend to form deposits of primary minerals, from ascending fluids, and supergene processes tend to form secondary minerals from descending fluids.

Ascending hot aqueous solutions originating in the magma contain ions derived from the magma itself, and also from leaching of surrounding rocks. As the solutions rise the temperature and pressure fall. Eventually a point is reached where the minerals start to crystallise out. Minerals formed in this way are primary minerals. Sulphur is a common component of the fluids, and most of the common ore metals, lead, zinc, copper, silver, molybdenum and mercury, occur chiefly as sulphide and sulfosalt minerals. Examples of primary minerals formed in this way include pyrite, galena, sphalerite and chalcopyrite

Processes due to circulation of meteoric water (water derived from snow and rain) are supergene processes. The descending meteoric waters oxidise the primary sulphide ore minerals and leach metals from the oxidised ore. As the fluids descend the dissolved substances may eventually precipitate to form two zones of secondary minerals, one above and the other below the water table. Conditions above the water table are usually oxidising. Secondary minerals that are stable under these conditions include malachite, azurite, cuprite, pyromorphite, and smithsonite. Beneath the water table conditions are usually reducing, and secondary minerals that form here are dominantly sulphides, such as covellite and chalcocite. Even native metals such as copper, copper may precipitate in this environment.
This region is called the zone of supergene enrichment, because the processes here produce secondary sulphides making the metal content of the rock higher than that of the primary ore. All such processes take place at essentially atmospheric conditions, 25°C and atmospheric pressure.

Acanthite

Formula: Ag2S sulphide
Specific gravity: 7.3
Hardness: 2
Streak: Black
Colour: Lead grey
Solubility: Acanthite is slightly soluble in hydrochloric acid and sulphuric acid.
Environments:

Hydrothermal environments

Acanthite is a primary silver mineral that occurs in epithermal (low temperature) hydrothermal silver ore veins. It may also be of secondary origin. At atmospheric pressure, acanthite is stable below 173°C. Above 173°C the structure changes to produce crystals of twinned acanthite, known as argentite. Argentite is unstable below 173°C, and if the temperature drops below this level it will change back to acanthite.

Common impurities: Se

Actinolite

Formula: ☐Ca2(Mg4.5-2.5Fe2+0.5-2.5Si8O22 (OH)2
Mg/(Mg + Fe2+) is 0.5 to 0.9, inosilicate (chain silicate) amphibole
Specific gravity: 3.03 to 3.24
Hardness: 5 to 6
Streak: White
Colour: Green, green-black, grey-green, or black. Colourless, pale green to deep green in thin section.
Solubility: Insoluble in water and hydrochloric acid
Environments:

Metamorphic environments
Hydrothermal environments

Actinolite is an amphibole mineral that is produced by low-grade regional or contact metamorphism of magnesium carbonate. Hydrothermal actinolite occurs in veins and as replacement of mafic minerals. In active geothermal systems hosted by intermediate to mafic volcanic rocks, actinolite is present at temperatures above 280oC.
It may be found in schist.
Associated minerals are calcite, quartz, epidote, glaucophane, pumpellyite and lawsonite.
Actinolite is a mineral of the albite-epidote-hornfels, prehnite-pumpellyite, greenschist, amphibolite and glaucophane-bearing blueschist facies.

At the Belvidere Mountain Complex in Vermont, USA, actinolite occurs in coarse-grained amphibolite, as pods along fault-zone contacts with serpentinite and as fine-grained masses with chlorite in fine-grained amphibolite.
In the Bronx, New York City, it occurs associated with quartz and calcite.

Actinolite may be altered to chlorite.

Common impurities: Mn, Al, Na, K, Ti

Adamite

Formula: Zn2(AsO4)(OH) arsenate
Specific gravity: 4.3 to 4.5
Hardness: 3½
Streak: White
Colour: Colourless, white, yellow, green (copper adamite), and pink to violet (cobalt adamite).
Solubility: Readily soluble in hydrochloric acid and sulphuric acid.

Environments:

Hydrothermal environments

Adamite is a secondary arsenate that occurs in the oxidation zone of high-temperature lode zinc- and arsenic-bearing hydrothermal mineral deposits, associated with azurite, goethite, hemimorphite, mimetite, olivinite, scorodite and smithsonite.
Adamite is abundant and widespread at the San Rafael Mine, Nevada, USA. It usually occurs alone there, but it has been found associated with wulfenite and smithsonite, or with segnitite and duftite.

Common impurities: Cu,Fe,Co

Adelite

Formula: CaMg(AsO4)(OH)
Anhydrous arsenate containing hydroxyl, adelite group
Specific gravity: 3.71 to 3.76
Hardness: 5
Streak: White
Colour: Colourless, white, grey, bluish grey, yellowish grey, yellow, pale green, pinkish brown, brown. Colourless in transmitted light
Solubility: Soluble in dilute acids
Environments:

Metamorphic environments

Adelite is a rare mineral found in a metamorphosed iron-manganese ore body at Långban, Sweden, associated with sarkinite, arsenoclasite, braunite, hedyphane, fredrikssonite and dolomite. At Jacobsberg and at the Kittel mine, Nordmark, Sweden, adelite occurs with hausmannite, magnetite and native copper. At Franklin, New Jersey, USA, adelite occurs in willemite-franklinite ore from a metamorphosed zinc orebody, associated with hodgkinsonite, baryte, allactite, rhodochrosite, franklinite, willemite and chlorophoenicite. At Sterling Hill, New Jersey, USA, adelite is associated with alleghanyite, kraisslite, sphalerite, rhodochrosite, willemite, franklinite, johnbaumite–svabite, zincite, baryte and calcite.

Common impurities: Pb,Mn,Na,Cu,Ba

Aegirine

Formula:NaFe3+Si2O6 inosilicate (chain silicate), pyroxene group
Specific gravity: 5.50 to 3.60
Hardness: 6
Streak: Pale yellowish grey
Colour: Black, brown, green. Bright green to yellow-green in thin section.
Solubility: Aegirine is slightly soluble in hydrochloric acid.
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites
Metamorphic environments

Aegirine is a pyroxene. It is a relatively rare primary mineral found chiefly in igneous rocks rich in Na and poor in SiO2 and in syenite pegmatites. It is also found as a secondary mineral in metamorphic rocks.
Aegirine may be found in granite, syenite, nepheline syenite, rhyolite and schist.
In igneous rocks it is associated with orthoclase, feldspathoids, augite and soda-rich amphibole.
In hornfels of contact metamorphic rocks it is found with quartz, spessartine and riebeckite.

Alteration

aegirine and CaO to andradite, quartz and Na2O
2NaFe3+Si2O6 + 3CaO → Ca3Fe3+2 (SiO4)3 + SiO2 + Na2O
This is a high temperature process.

aegirine, epidote and CO2 to albite, hematite, quartz, calcite and H2O
4NaFe3+Si2O6 + 2Ca2(Al2Fe3+ [Si2O7](SiO4)O(OH) + 4CO2 → 4Na(AlSi3O8) + 3Fe2O3 + 2SiO2 + 4CaCO3 + H2O

albite, diopside and magnetite to aegirine, Si2O6, garnet and quartz
2Na(AlSi3O8) + CaMgSi2O6 + Fe2+Fe3+2O4 ⇌ 2NaFe3+Si2O6 + Si2O6 + CaMgFe2+Al2(SiO4)3 + SiO2
This reaction may occur in blueschist facies rocks in Japan.

serpentine, aegirine and quartz to magnesio-riebeckite and H2O
Mg3Si2O5(OH)4 + 2NaFe3+Si2O6 + 2SiO2 → Na2 (Mg3Fe3+2)Si8O22(OH)2 + H2O

titanomagnetite (ilmenite combined with magnetite), quartz, and aegirine-hedenbergite to aenigmatite, hedenbergite, magnetite and O2
6(Fe2+Ti4+O3 + Fe2+Fe3+2O4) + 12SiO2 + 12(NaFe3+Si2O6 + CaFe2+Si2O6) ⇌ 3Na4[Fe2+10Ti2]O4[Si12O36] + 12CaFe2+Si2O6 + 2Fe2+Fe3+2O4 + 5O2

jadeite, diopside, magnetite and quartz to aegirine, kushiroite (pyroxene) and hypersthene
2NaAlSi2O6 + CaMgSi2O6 + Fe2+Fe3+2O4 + SiO2 ⇌ 2NaFe3+Si2O6 + CaAlAlSiO6 + MgFeSi2O6
Aegirine in blueschist facies rocks may be formed by the above reaction.

Common impurities: Al,Ti,V,Mn,Mg,Ca,K,Zr,Ce

Aenigmatite

Formula: Na4[Fe2+10Ti2]O4[Si12O36] inosilicate (chain silicate)
Specific gravity: 3.74 to 3.85
Hardness: 5½ to 6
Streak: reddish brown
Colour: velvet-black
Solubility: soluble in HF
Environments:

Plutonic igneous environments
Volcanic igneous environments

Aenigmatite is a rock-forming mineral, relatively common in sodium rich alkaline rocks. It occurs in nepheline and sodalite syenites, and occasionally in alkali granite. It also occurs in phenocrysts and in the groundmass of alkaline lavas, such as trachyte.
Common associates: aegirine, arfvedsonite, augite, fayalite, hedenbergite, ilmenite and riebeckite

Alteration

aenigmatite, anorthite and O2 to hedenbergite, albite, ilmenite and magnetite
½Na4[Fe2+10Ti2]O4[Si12O36] + CaAl2Si2O8 + ½O2 = CaFe2+Si2O6 + 2NaAlSi3O8 + Fe2+Ti4+O3 + Fe2+Fe3+2O4

titanomagnetite (ilmenite combined with magnetite), quartz, and aegirine-hedenbergite to aenigmatite, hedenbergite, magnetite and O2
6(Fe2+Ti4+O3 + Fe2+Fe3+2O4) + 12SiO2 + 12(NaFe3+Si2O6 + CaFe2+Si2O6) ⇌ 3Na4[Fe2+10Ti2]O4[Si12O36] + 12CaFe2+Si2O6 + 2Fe2+Fe3+2O4 + 5O2

Common impurities: Al,Mn,Mg,Ca,K,Cl

Agardite

Formulae
agardite-(Ce): CeCu2+6(AsO4)3(OH)6.3H2O
agardite-(La): LaCu2+6(AsO4)3(OH)6.3H2O
agardite-(Nd): NdCu2+6(AsO4)3(OH)6.3H2O
agardite-(Y): YCu2+6(AsO4)3(OH)6.3H2O
Specific gravity: Agardite-(Ce) 3.7, Agardite-(La) 3.65, Agardite-(Nd) 3.72, Agardite-(Y) 3.61 to 3.72
Hardness: 3 to 4 (all)
Streak: Greenish white (all)
Colour: Agardite-(Ce) Light green, yellowish green, Agardite-(La) Grass-green to dull green, yellowish green to intense bluish green, rarely nearly colourless, Agardite-(Nd) Grass-green, greenish, greenish-blue, Agardite-(Y) Bluish green to yellow green
Solubility: Agardite-(Y) is soluble in hydrochloric acid
Environments:

Hydrothermal environments

Agardite-(Ce) is an oxidation product formed on baryte and quartz.
Agardite-(La) was found in a fluorite mine associated with quartz, fluorite, bastnäsite-(Ce) and baryte.
Agardite-(Y) occurs in the oxidation zone of copper veins or deposits. At the Bou Skour Mine, Ouazazate, Morocco it occurs in the oxidation zone associated with azurite, malachite, cuprite, native copper and quartz. At Laurium, Attica, Greece it is associated with smithsonite and aurichalcite.

Ajoite

Formula: K3Cu2+20Al3Si29O76(OH)16.8H2O unclassified silicate
Specific gravity: 2.96
Streak: Greenish white
Colour: Bluish green
Solubility: Readily decomposed by acids such as hydrochloric and nitric leaving a coherent white mass of hydrated silica.
Environments:

Hydrothermal environments

Ajoite is a secondary copper mineral that occurs in oxidised copper-rich deposits. It is found in massive fracture coatings, vein fillings, vugs, associated with shattuckite, quartz, muscovite variety sericite and pyrite.

Localities

Mexico

Munihuaza, Mexico: Ajoite is associated with shattuckite, mottramite variety duhamelite and sillénite.

South Africa

Messina, South Africa: Ajoite is found as inclusions in quartz and associated with quartz and papagoite.

USA

Potter-Cramer property, Maricopa County, Arizona, USA: Ajoite is associated with creaseyite and fluorite.

New Cornelia Mine, Ajo, Pima County, Arizona, USA (type locality): Ahoite is associated with shattuckite, quartz, pyrite, muscovite and conichalcite.

Alteration: Ajoite may form as an alteration product of shattuckite, and also it may itself alter to shattuckite.

Common impurities: Fe,Mn,Ca

Åkermanite

Formula:Ca2MgSi2O7 sorosilicate (Si2O7 groups), melilite group
Near end-member åkermanite is very rare, possibly unknown in nature.
Specific gravity: 2.90 to 2.97
Hardness: 5 to 6
Streak: White
Colour: Colourless, grey, green, brown
Melting point: 1,454oC at a pressure of 1 kbar
Environments:

Plutonic igneous environments
Metamorphic environments

Commonly found in slags. Åkermanite is a product of contact metamorphism of siliceous limestone and dolostone, and it also forms from alkalic magmas rich in calcium.
It is a common component of skarn, and a mineral of the sanidinite and granulite facies.

Alteration

As åkermanite cools from its melting point it is stable down to 1345oC, when the stable mixture is åkermanite and wollastonite. From 1240oC down to 1050oC a mixture of åkermanite, wollastonite and diopside is stable, and at lower temperatures åkermanite dissociates to form wollastonite and monticellite. The stability of åkermanite is limited to pressures of less than 14 kbar in an anhydrous environment, and less than 10.2 kbar with excess H2O.

åkermanite to wollastonite and monticellite
Ca2MgSi2O7 ⇌ CaSiO3 + CaMgSiO4
The forward reaction occurs at temperature less than 1,050oC.

åkermanite and CO2 to diopside and calcite
Ca2MgSi2O7 + CO2 ⇌ CaMgSi2O6 + CaCO3
The maximum stability limit of åkermanite in the presence of excess CO2 is about 6 kbar. Below that pressure, at relatively lower temperatures, åkermanite reacts with CO2 to form diopside and calcite according to the above reaction.

diopside and monticellite to åkermanite and forsterite
CaMgSi2O6 + 3CaMgSiO4 ⇌ 2Ca2MgSi2O7 + Mg2SiO4

monticellite and CO2 to åkermanite, forsterite and calcite
3CaMgSiO4 + CO2 ⇌ Ca2MgSi2O7 + Mg2O7 + CaCO3
At 4.3 kbar pressure the equilibrium temperature is about 890oC (granulite facies).

monticellite and diopside to åkermanite and forsterite
3CaMgSiO4 + CaMgSi2O6 ⇌ 2Ca2MgSi27 + Mg2O7
Monticellite is stable below 890oC at pressure of about 4.3 kbar (granulite facies).

Alabandite

Formula: MnS
Sulphide, galena group
Specific gravity: 4.0 to 4.1
Hardness: 3½ to 4
Streak: Green
Colour: Black, tarnishing to brown
Environments

Hydrothermal environments

Alabandite occurs in epithermal polymetallic sulphide veins and especially in low-temperature manganese deposits . It is an accessory mineral in some enstatite chondrodites . In hydrothermal veins it is commonly associated with galena, chalcopyrite, sphalerite, pyrite, acanthite, rhodochrosite, calcite, rhodonite and quartz. At Broken Hill, New South Wales, Australia, alabandite is associated with calcite, baryte, pyrite, chabazite and sulphur. At the Uchacchacua mine, Lima Department, Peru, alabandite is associated with fluorite, proustite and rhodochrosite, and at the Sunnyside mine, San Juan County, Colorado, USA, it is associated with friedelite and alleghanyite.

Common impurities: Fe,Mg,Co

Alamosite

Formula: PbSiO3 inosilicate (chain silicate)
Specific gravity: 6.49
Hardness: 4½
Streak: White
Colour: Colourless to white
Solubility: Gelatinises with acids
Environments

Hydrothermal environments

Alamosite is a rare secondary mineral found in the oxidised zone of lead-bearing deposits.

Localities

Mexico

Álamos, Mexico (type locality): Alamosite is associated with wulfenite, leadhillite and cerussite.

Namibia

Tsumeb, Namibia: Alamosite is associated with leadhillite, anglesite, melanotekite, fleischerite, kegelite and hematite.

USA

Rawhise mine, Arizona, USA: Alamosite is associated with melanotekite, shattuckite and wickenburgite.

Tiger, Arizona, USA: Alamosite is associated with diaboleite, phosgenite, cerussite, wulfenite and willemite.

Common impurities: Al,Fe,Mn,Ca

Albite

Formula: Na(AlSi3O8) tectosilicate (framework silicate)
albite is a plagioclase feldspar.
Andesine is a variety of albite rarely found except as grains in andesite.
Cleavelandite is a platy variety of albite, generally found in pegmatites.
Oligoclase is a variety of albite belonging to the amphibolite facies.
Specific gravity: 2.60 to 2.65
Hardness: 6 to 6½
Streak: White
Colour: Colourless, white
Melting point (albite): About 1,100oC at atmospheric pressure
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments (albite):

Pegmatites
Carbonatites
Metamorphic environments

Albite is a primary mineral crystallising at the low temperature end of the continuous arm of the Bowen reaction series. It is a plagioclase feldspar found in pegmatites and carbonatites. It is a secondary mineral in contact and regional metamorphic environments.
Intrusion-related albite is found in the core of some porphyry (rock with coarse phenocrysts in a finer groundmass) systems associated with alkaline or felsic intrusions.
Albite is a common but not essential constituent of granite and granite pegmatites.
It also may be found in metamorphosed quartz sandstone, rhyolite, trachyte, hornfels, phyllite and schist.
In nepheline syenite pegmatites and carbonatites albite is associated with acmite and nepheline.
In rhyolite and trachyte it may replace earlier microcline.
Albite is characteristic of the zeolite and albite-epidote-hornfels facies. It is also a mineral of the prehnite-pumpellyite, greenschist, amphibolite and blueschist facies.
Environments (andesine):

Plutonic igneous environments
Sedimentary environments
Metamorphic environments

Andesine is widespread in igneous rocks of intermediate silica content, such as syenite and andesite. It is characteristic of the amphibolite and granulite facies. It is rarely found except as grains in andesite (where it may be associated with augite) and diorite.
Environments (oligoclase):

Plutonic igneous environments
Pegmatites
Metamorphic environments

Oligoclase is a common but not essential constituent of granodiorite.
It also may be found in granite, monzonite, gabbro, anorthosite and in gneiss with biotite and hornblende.
It is a mineral of the amphibolite and granulite facies.
Andesine and oligoclase occur towards the higher temperature range of albite and its varieties.

Alteration

aegirine, epidote and CO2 to albite, hematite, quartz, calcite and H2O
4NaFe3+Si2O6 + 2Ca2(Al2Fe3+ [Si2O7](SiO4)O(OH) + 4CO2 → 4Na(AlSi3O8) + 3Fe2O3 + 2SiO2 + 4CaCO3 + H2O

aenigmatite, anorthite and O2 to hedenbergite, albite, ilmenite and magnetite
½Na4[Fe2+10Ti2]O4[Si12O36] + CaAl2Si2O8 + ½O2 = CaFe2+Si2O6 + 2NaAlSi3O8 + Fe2+Ti4+O3 + Fe2+Fe3+2O4

albite to nepheline and quartz
Na(AlSi3O8) ⇌ NaAlSiO4 + 2SiO2

albite and NaCl (aqueous) to sodalite and silica
6Na(AlSi3O8) + 2NaCl → 2Na4(Si3Al3)O12Cl + 12SiO2

albite, chlorite and calcite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz, CO2 and H2O
8Na(AlSi3O8) + (Mg4.0Fe2.0)(AlSi3O10)(OH)8 + CaCO3 → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 2SiO2 + CO2 + 2H2O
In low to intermediate metamorphism jadeite-glaucophane assemblages may arise from reactions such as the one above.

albite, diopside and magnetite to aegirine, Si2O6, garnet and quartz
2Na(AlSi3O8) + CaMgSi2O6 + Fe2+Fe3+2O4 ⇌ 2NaFe3+Si2O6 + Si2O6 + CaMgFe2+Al2(SiO4)3 + SiO2
This reaction may occur in blueschist facies rocks in Japan.

albite and montmorillonite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz and H2O
8Na(AlSi3O8) + 2Ca0.5(Mg3.5Al0.5)Si8O20(OH)4.nH2O → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 15SiO2 + 6H2O
This reaction occurs in low to intermediate metatmorphism.

amphibole, clinozoisite, chlorite, albite, ilmenite and quartz to garnet, omphacite, rutile and H2O
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + 2Ca2Al3[Si2o7][SiO4]O(OH) + Mg5Al(AlSi3O10)(OH)8 + 3NaAlSi3O8 + 4Fe2+Ti4+O3 + 3SiO2 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 6H2O
In low-grade rocks relatively poor in calcite the garnet-omphacite association may be developed by the above reaction.

analcime and quartz to albite and H2O
Na(AlSi2O6).H2O + SiO2 ⇌ Na(AlSi3O8) + H2O

anorthite, albite and H2O to jadeite, lawsonite and quartz
CaAl2 Si2O8 + NaAlSi3O8 + 2H2O → NaAlSi2O6 + CaAl2(Si2O7)(OH)2.H2 + SiO2

augite, albite, pyroxene, anorthite and ilmenite to omphacite, garnet, quartz and rutile
2MgFe2+Si2O6 + Na(AlSi3O8) + Ca2Mg2Fe2+Fe3+AlSi5O18 + 2Ca(Al2Si2O8) + 2Fe2+Ti4+O3 → NaCa2MgFe2+Al(Si2O6)3 + (Ca2Mg3Fe2+4)(Fe3+Al5)(SiO4)9 + SiO2 + 2TiO2
This reaction occurs at high temperature and pressure.

diopside and albite to omphacite and quartz
CaMgSi2O6 + xNaAlSi3O8 ⇌ CaMgSi2O6.xNaAlSi2O6 + SiO2

enstatite-ferrosilite, diopside-hedenbergite, albite, anorthite and H2O to amphibole and quartz
+ Ca(Al2Si2O8) + H2O ⇌ NaCa2(Mg,Fe)4Al(Al2O6)O22(OH)2 + 4SiO2
This reaction represents metamorphic reactions between the granulite and amphibolite facies.

enstatite-ferrosilite, diopside-hedenbergite, albite, anorthite and H2O to amphibole and quartz
3(Mg,Fe2+)SiO3 + Ca(Mg,Fe2+)Si2O6 + NaAlSi3O8 + Ca(Al2Si2O8) + H2O ⇌ NaCa2(Mg,Fe)4Al(Al2O6)O22(OH)2 + 4SiO2
This reaction represents metamorphic reactions between the granulite and amphibolite facies.

jadeite to nepheline and albite
2NaAlSi2O6 ⇌ NaAlSiO4 + NaAlSi3O8
At 20 kbar pressure the equilibrium temperature is about 1,000oC (eclogite facies), with equilibrium to the right at higher temperatures and to the left at lower temperatures.

Jadeite and quartz to albite
NaAlSi2O6 + SiO2 ⇌ NaAlSi3O8
The equilibrium temperature for this reaction at 10 kbar pressure is about 400oC (blueschist facies), and at 26 kbar the equilibrium temperature is 1,000oC (eclogite facies). For any given pressure the equilibrium is to the right at higher temperatures, and to the left at lower temperatures, and for any given temperature the equilibrium is to the left at higher pressures and to the right at lower pressures.

labradorite, albite, forsterite and diopside to omphacite, garnet and quartz
3CaAl2Si2O8 + 2Na(AlSi3O8) + 3Mg2SiO4 + nCaMgSi2O6 → (2NaAlSi2O6 + nCaMgSi2O6) + 3(CaMg2)Al2(SiO4)3 + 2SiO2
This reaction occurs at high temperature and pressure.

nepheline and diopside to melilite, forsterite and albite
3NaAlSiO4 + 8CaMgSi2O6 ⇌ 4Ca2MgSi2O7 + 2Mg2SiO4 + 3NaAlSi3O8
This reaction is in equilibrium at about 1180oC, with lower temperatures favouring the forward reaction.

spodumene and Na+ to eucryptite, albite and Li+
2LiAlSi2O6 + Na+ → LiAlSiO4 + NaAlSi3O8 + Li+
Whether spodumene breaks down into albite or into eucryptite and albite depends largely on the presence or absence of quartz.

spodumene, quartz and Na+ to albite and Li+
LiAlSi2O6 + SiO2 + Na+ → NaAlSi3O8 + Li+
Whether spodumene breaks down into albite or into eucryptite and albite depends largely on the presence or absence of quartz.

Common impurities: Ca,K,Mg

Alleghanyite

Formula: Mn2+5(SiO4)2(OH)2 nesosilicate (insular SiO4 groups) humite group
Alleghanyite forms a discontinuous solid solution with chondrodite.
Epitaxy: Leucophanite has been found as an epitaxial growth on alleghanyite.
Specific gravity: 3.93 to 4.02
Hardness: 5 to 5½
Streak: Very pale pink
Colour: Pinkish to reddish brown, deep pink, greyish pink
Solubility: Soluble in hydrochloric acid leaving a silica gel
Environments:

Metamorphic environments
Hydrothermal environments

Alleghanyite requires water-rich conditions to form in silica-undersaturated rocks during regional metamorphism. It occurs in manganese-rich skarn with other manganese silicates and carbonates, and it is also hydrothermally deposited in lenses in manganese-bearing veins with tephroite and spessartine.

Alteration

manganhumite and H2O to alleghanyite and quartz
5Mn7(OH)2(SiO4)3 + 2H2O = 7Mn5(OH)2(SiO4)2 + SiO2

manganhumite and rhodochrosite and H2O to alleghanyite and CO2
2Mn7(OH)2(SiO4)3 + MnCO3 = 3Mn5(OH)2(SiO4)2 + CO2

Common impurities: Ti,Al,Fe,Mg,Ca,F

Localities

USA

San Jose mine, California, USA: Alleghanyite has been found in a boulder with tephroite, hausmannite, pyrochroite, ganophyllite, rhodochrosite, baryte, psilomelane and alabandite.

Franklin/Sterling Hill, New Jersey, USA: Alleghanyite occurs as isolated crystals in the Franklin marble, and also in veins cross-cutting franklinite ore near pegmatites in a metamorphosed stratiform Zn-Mn deposit, formed in apparent equilibrium with rare species such as kolicite, holdenite, magnussonite, adelite, kraisslite and chlorophoenicite. Aside from these uncommon arsenates, other species associated with alleghanyite are franklinite, willemite, baryte and carbonates, all of secondary origin. At this locality alleghanyite always has some zinc content, but never more than 0.2 Zn per 2 Si. Some alleghanyite co-exists with zincite, but mostly willemite is the only associated zinc phase. Material from Sterling Hill is ver rich in magnesium.

Bald Knob, North Carolina, USA (type locality): The environment is probably metamorphosed sediment with an estimated temperature of formation 575 +/- 40oC, pressure 5 +/- 1 kbar. Alleghanyite occurs here in lenses in a manganese-bearing calcite, mostly as grains embedded in the calcite and commonly intergrown with galaxite. It is chemically incompatible with quartz, and does not occur here associated either with quartz or with tephroite, although tephroite also occurs at this locality. .

Allophane

Formula: Al2O3(SiO2)1.3-2.0.2.5-3.0H2O phyllosilicate (sheet silicate), allophane group
Specific gravity: 1.8 to 2.78
Hardness: 3
Streak: White
Colour: White, pale blue to sky-blue, green, brown
Solubility: Gelatinises in hydrochloric acid
Environments:

Sedimentary environments
Hydrothermal environments

Allophane is principally a weathering product of volcanic ash, and also a hydrothermal alteration product of feldspar. It may be a precursor to halloysite, but halloysite also alters to allophane. Allophane is frequently found with admixed halloysite, imogolite, limonite, opal, gibbsite and cristobalite, and occasionally with chrysocolla or evansite.
Common impurities: Ti,Fe,Mg,Ca,Na,K

Almandine

Almandine is the commonest mineral of the garnet group.
Formula: Fe2+3Al2(SiO4)3 nesosilicate (insular SiO4 groups)
Specific gravity: 4.318
Hardness: 7 to 7½
Streak: White
Colour: Red, black
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments:

Plutonic igneous environments
Pegmatites
Metamorphic environments (common)

Almandine is the common garnet in metamorphic rocks, typically occuring in mica schist and gneiss, resulting from the regional metamorphism of argillaceous (clay-rich) sediments. It also occurs in contact metamorphic hornfels, and occasionally in diorite. It is stable over a wide range of pressure-temperature conditions. Metamorphic almandine is a mineral of the hornblende-hornfels, amphibolite, granulite, blueschist and eclogite facies.

Alteration

almandine and phlogopite to pyrope and annite
Fe2+3Al2(SiO4)3 + KMg3AlSi3O12(OH)2 ⇌ Mg3Al2Si3O12 + KFe3AlSi3O10(OH)2
Both temperature and pressure affect the equilibrium of this reaction, but temperature is more significant. This assemblage is commonly formed during amphibolite facies metamorphism of pelitic rocks.

calcium amphibole, grossular and quartz to diopside- hedenbergite, anorthite, pyrope-almandine and H2O
2Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + Ca3Al2(SiO4)3 + SiO2 = 3Ca(Fe,Mg)Si2O6 + 4Ca(Al2Si2O8) + (Mg,Fe2+)3Al2(SiO4)3 + 2H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

chloritoid and quartz to staurolite, almandine and H2O
23Fe2+Al2O(SiO4)(OH)2 + 8SiO2 ⇌ 4Fe2+2Al9Si4O23(OH) + 5Fe2+3Al2(SiO4)3 + 21H2O

hornblende, grossular and quartz to Fe-rich diopside, anorthite, almandine and H2O
2Ca2(Mg,Fe2+)3(Al4Si6)O22(OH)2 + Ca3Al2Si3O12 + 2SiO2 = 3Ca(Mg,Fe2+)Si2O6 + 4CaAl2Si2O8 + (Mg,Fe2+)Al2Si3O12 + 2H2O
Fe-rich diopside occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies. The above reaction is typical.

Amblygonite

Formula: LiAl(PO4)F phosphate
Specific gravity: 3.0 to 3.1
Hardness: 6
Streak: White
Colour: White, grey, yellow to brown, greenish, bluish
Solubility: Amblygonite is slightly soluble in hydrochloric, sulphuric and nitric acid
Environments:

Plutonic igneous environments
Pegmatites

Amblygonite is a rare mineral typically found in lithium-rich granite pegmatites with spodumene, tourmaline, lepidolite and apatite.

Amphibole

Amphiboles are double chain inosilicates, such as
actinolite ☐Ca2(Mg4.5-2.5Fe2+0.5-2.5Si8O22(OH)2 ☐Ca2(Mg4.5-2.5Fe2+0.5-2.5)Si8O22 (OH)2,
edenite NaCa2Mg5(Si7Al)O22(OH)2,
hornblende ☐Ca2(Fe2+4Al)(Si7Al)O22(OH)2,
pargasite NaCa2(Mg4Al)(Si6Al2)O22(OH)2 and
tremolite ☐Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22 (OH)2.
In the discontinuous branch of the Bowen reaction series amphibole is intermediate between pyroxene (higher temperature) and biotite (lower temperature).
Environments:

Plutonic igneous environments

Amphibole is typical of plutonic igneous environments.
Amphibole is a common but not essential constituent of rhyolite and gneiss.
It also may be found in granite, quartzolite, gneiss and eclogite.
Amphibole is the characteristic mineral of the amphibolite facies; it is never found in the granulite facies.

Alteration

Ca-Fe amphibole and anorthite to chlorite, epidote and quartz
CaFe5Al2Si7O22(OH)2 + 3CaAl2Si2O8 + 4H2O → Fe5Al2Si3O10(OH)8 + 2Ca2Al3Si3O12(OH) + 4SiO2

calcium amphibole, calcite and quartz to diopside- hedenbergite, anorthite, CO2 and H2O
Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + 3CaCO3 + 4SiO2 = 3Ca(Fe,Mg)Si2O6 + 2Ca(Al2Si2O8) + 3CO2 + H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

calcium amphibole, grossular and quartz to diopside- hedenbergite, anorthite, pyrope-almandine and H2O
2Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + Ca3Al2(SiO4)3 + SiO2 = 3Ca(Fe,Mg)Si2O6 + 4Ca(Al2Si2O8) + (Mg,Fe2+)3Al2(SiO4)3 + 2H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

amphibole, chlorite, paragonite, ilmenite, quartz and calcite to garnet, omphacite, rutile, H2O and CO2
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + Mg5Al(AlSi3O10)(OH)8 + 3NaAl2(Si3Al)O10(OH)2 + 4Fe2+Ti4+O3 + 9SiO2 + 4CaCO3 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 8H2O + 4CO2
In low-grade rocks relatively rich in calcite the garnet-omphacite association may be due to reactions such as the above.

amphibole, clinozoisite, chlorite, albite, ilmenite and quartz to garnet, omphacite, rutile and H2O
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + 2Ca2Al3[Si2o7][SiO4]O(OH) + Mg5Al(AlSi3O10)(OH)8 + 3NaAlSi3O8 + 4Fe2+Ti4+O3 + 3SiO2 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 6H2O
In low-grade rocks relatively poor in calcite the garnet-omphacite association may be developed by the above reaction.

enstatite-ferrosilite, diopside-hedenbergite, albite, anorthite and H2O to amphibole and quartz
3(Mg,Fe2+)SiO3 + Ca(Mg,Fe2+)Si2O6 + NaAlSi3O8 + Ca(Al2Si2O8) + H2O ⇌ NaCa2(Mg,Fe)4Al(Al2O6)O22(OH)2 + 4SiO2
This reaction represents metamorphic reactions between the granulite and amphibolite facies, and it is the reason why amphibole is never found in granulite facies rocks.

Analcime

Formula: Na(AlSi2O6).H2O
Tectosilicate (framework silicate), zeolite group, feldspathoid
Specific gravity: 2.24 to 2.29
Hardness: 5 to 5½
Streak: White
Colour: White, colourless, gray, pink, greenish, yellowish; colourless in thin section.
Solubility: Moderately soluble in hydrochloric acid
Environments:

Volcanic igneous environments
Pegmatites
Sedimentary environments
Basaltic cavities

Analcime occurs as a primary mineral in some igneous rocks; it is the only zeolite that crystallises directly from molten rock. It is also the product of hydrothermal action in the filling of basalt cavities, where analcime phenocrysts crystallise in deep basaltic magma chambers at temperatures between 600oC and 640oC, and pressure between 5 and 13 kbar, in associations with prehnite, calcite and zeolites such as chabazite, thomsonite and stilbite. Geothermal wells have been drilled through a thick series of basalt flows in western Iceland, where it was found that analcime crystallised at temperatures from to 300oC at depths between 72m and 1600m. Analcime may occur in mafic rocks such as aegirine-analcime-nepheline syenite. In lake beds, it may be altered from pyroclastics or clay minerals, or it may be a primary precipitate. It is authigenic (formed in place) in sandstone and siltstone.

In the alkaline rocks of the Kola peninsula, Russia, analcime is associated with aegirine and may be either primary or secondary after sodalite or aegirine.

At the Bearpaw Mountains, Montana, USA, analcime occurs in cavities in igneous rock, associated with axinite, prehnite and datolite.

Alteration

analcime and quartz to albite and H2O
Na(AlSi2O6).H2O + SiO2 ⇌ Na(AlSi3O8) + H2O

nepheline and H4SiO4 (silicic acid) to analcime and H2O
NaAlSiO4 + H4SiO4 ⇌ Na(AlSi2O6).H2O + H2O

Localities

Australia

In Western Tasmania analcime occurs as a late stage primary mineral with gonnardite-natrolite and as an alteration product of feldspar. It also occurs in basaltic cavities.

Iran

In the vicinity of Meshkinshahr, Ardabil Province, crystals of analcime are found embedded in small amygdules in potassium-rich basalt, associated with chabazite, mesolite and/or thomsonite. The analcime originated hydrothermally.

At Mount Kahoven, Semnan Province, orange coloured crystals of analcime are found on perched on vesicular basalt.

South Africa

At Palabora analcime is an early phase in the deepest parts of the dyke fracture zone. Crystal cores may have originally been wairakite overgrown by analcime, then later hydrothermal alteration converted wairakite to laumontite. A later generation of analcime occurs on fluorapophyllite.

Andalusite

Formula: Al2OSiO4 nesosilicate (insular SiO4 groups). Polymorph (same formula, different structure) of kyanite and sillimanite.
Specific gravity: 3.13 to 3.16
Hardness: 6½ to 7½
Streak: White
Colour: Pink, brown, white, grey, violet, yellow, green and blue
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Plutonic igneous environments (rarely)
Pegmatites (rarely)
Metamorphic environments (typical)
Hydrothermal replacement environments

Andalusite is found typically as a product of contact metamorphism of argillaceous (clay-rich) rocks, where it is often associated with cordierite. It also occurs occasionally in igneous rocks.
In high temperature assemblages andalusite may coexist with corundum.
Andalusite occurs in granite, gneiss, phyllite and schist.
It is a mineral of the albite-epidote-hornfels, hornblende-hornfels, pyroxene-hornfels, amphibolite and granulite facies.

Alteration

Aluminium silicate stability diagram Andalusite, sillimanite and kyanite are polymorphs (same formula, different structure); they are in equilibrium at a pressure of 3.75 kbar and temperature 504oC (amphibolite facies).
Andalusite is unstable at high pressure and cannot form at pressure above 3.75 kbar

augite and andalusite to enstatite- ferrosilite and anorthite
Ca(Fe,Mg)Si2O6 +Al2SiO5 → (Mg,Fe2+)SiO3 + Ca(Al2Si2O8)

enstatite-ferrosilite and andalusite to Fe rich cordierite and spinel- hercynite
5(Mg,Fe2+)SiO3 + 5 Al2SiO5 → 2(Mg,Fe2+)2Al4Si5O18 + (Mg,Fe2+)Al2O4
In medium-grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content, in an SiO2 deficient environment the association of andalusite with enstatite- ferrosilite is excluded by the above reaction.

enstatite-ferrosilite, andalusite and quartz to Fe-rich cordierite
2(Mg,Fe2+)SiO3 + 2Al2SiO5 + SiO2 → (Mg,Fe2+)2Al4Si5O18
In medium-grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content, the association of andalusite with enstatite- ferrosilite is excluded by the above reaction.

kaolinite to andalusite, pyrophyllite and H2O
3Al2Si2O5(OH)4 ⇌ 2Al2OSiO4 + Al2Si4O10(OH)2 + 5H2O
At 1 kbar pressure the equilibrium temperature for the reaction is about 320oC (albite-epidote-hornfels facies), with the equilibrium to the right at higher temperatures and to the left at lower temperatures.

kaolinite and diaspore to andalusite and H2O
Al2Si2O5(OH)4 + 2AlO(OH) ⇌ 2Al2OSiO4 + 3H2O
At 1 kbar pressure the equilibrium temperature for the reaction is about 320oC (albite-epidote-hornfels facies), with the equilibrium to the right at higher temperatures and to the left at lower temperatures.

margarite and quartz to anorthite, andalusite and H2O
CaAl2(Al2Si2O10)(OH)2 + SiO2 ⇌ Ca(Al2Si2O8) + Al2OSiO4 + H2O
The equilibrium temperature for this reaction at 2 kbar pressure is about 440oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

pyrophyllite to andalusite, quartz and H2O
Al2Si4O10(OH)2 ⇌ Al2SiO5 + 3SiO2 + H2O
The equilibrium temperature for this reaction at 1.8 kbar pressure is 414oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

pyrophyllite and diaspore to andalusite and H2O
Al2Si4O10(OH)2 + 6AlO(OH) ⇌ 4Al2SiO5 + 4H2O
This reacton is a low pressure reaction, occurring below about 1.9 kbar. Increasing temperature favours the forward reaction.

Andradite

Formula: Ca3Fe3+2(SiO4)3 nesosilicate (insular SiO4 groups), garnet group
Specific gravity: 3.8 to 3.9
Hardness: 6½ to 7
Streak: White
Colour: Yellow, greenish yellow to emerald-green, dark green; brown, brownish red, brownish yellow; grayish black, or black
Solubility: Andradite is slightly soluble in hydrochloric acid
Environments:

Pegmatites
Carbonatites
Metamorphic environments (typical)

Andradite typically occurs in contact or thermally metamorphosed impure calcium-rich sediments and particularly in skarn deposits often associated with such metamorphism. In contact metamorphic rocks it may be associated with danburite.

Alteration

aegirine and CaO to andradite, quartz and Na2O
2NaFe3+Si2O6 + 3CaO → Ca3Fe3+2 (SiO4)3 + SiO2 + Na2O This is a high temperature process.

calcite, hematite and CO2 quartz to andradite and
3CaCO3 + Fe2O3 + 3SiO2 → Ca3Fe3+2Si3O12 + 3CO2

hematite, wüstite, quartz and calcite to andradite, hedenbergite, magnetite and CO2
2Fe2O3 + 2FeO + 5SiO2 + 4CaCO3 → Ca3Fe3+2(SiO4)3 + CaFe2+Si2O6 +Fe2+Fe3+2O4 +4CO2

Common impurities: Ti,Cr,Al,Mg

Anglesite

Formula: Pb(SO4) sulphate
Specific gravity: 6.37 to 6.39
Hardness: 2½ to 3
Streak: White
Colour: Colourless, white, yellow, green; colourless in transmitted light.
Solubility: Anglesite is not very soluble in water.
Environments:

Hydrothermal environments

Anglesite is a common high temperature secondary mineral in the oxidation zone of hydrothermal replacement deposits rich in lead.
Lead will generally precipitate as primary galena from ore fluids rich in sulphur and lead. Removal of sulphur by precipitation of sulphides, however, may lead ultimately to an ore fluid from which galena cannot be precipitated, even with a high concentration of lead in solution. In these circumstances, anglesite, as well as cerussite and pyromorphite, could be precipitated as a primary mineral.
Anglesite is commonly associated with galena, cerussite, sphalerite, smithsonite, hemimorphite and iron oxides.

Alteration

In the oxidation zone, oxidation of pyrite forms ferrous (divalent) sulphate and sulphuric acid:
pyrite + oxygen + water → ferric sulphate + sulphuric acid
FeS2 + 7O + H2O → FeSO4 + H2SO4
The ferrous (divalent) sulphate readily oxidizes to ferric (trivalent) sulphate and ferric hydroxide:
ferrous sulphate + oxygen + water → ferric sulphate + ferric hydroxide
6FeSO4 + 3O + 3H2O → 2Fe2(SO4)3 + 2Fe(OH)3
Ferric sulfate is a strong oxidizing agent; it attacks galena as below.

galena, ferric sulphate, water and oxygen to anglesite, ferrous sulphate and sulphuric acid
PbS + Fe2(SO4)3 + H2O + 3O → PbSO4 + 2FeSO4 + H2SO4
Galena is oxidised to anglesite and ferric iron is reduced to ferrous iron.

galena and oxygen to anglesite
In air, at outcrops of galena,
PbS + 2O2 → PbSO4
At ordinary temperatures the equilibrium is displaced far to the right, and the apparent stability of galena is a result of the slowness of the oxidation.

Galena may also dissolve in carbonic acid from percolating rainwater to form hydrogen sulphide, which is then oxidised to form anglesite.
galena and carbonic acid to Pb2+, hydrogen sulphide and HCO3-
PbS + 2H2CO3 → Pb2+ + H2S + 2HCO3>-

hydrogen sulphide, oxygen, Pb2+ and HCO3>- to anglesite and carbonic acid
H2S + 2O2 + Pb2+ + 2HCO3>- → PbSO4 + 2H2CO3

Common impurities: Ba, Cu

Anhydrite

Formula: Ca(SO4) sulphate
Specific gravity: 2.98
Hardness: 3 to 3½
Streak: White
Colour: Colourless, white, grey, blue
Solubility: Moderately soluble in hydrochloric, sulphuric and nitric acid
Environments:

Carbonatites
Sedimentary environments (typical)
Hydrothermal environments

Anhydrite occurs in the oxidation zone of high temperature hydrothermal replacement deposits, in salt deposits, sediments and in some zeolite occurrences. It is often associated with gypsum but is not nearly so common. It is found in limestone and in some amygdaloidal cavities in basalt.
It is a common alteration mineral in some porphyry (rock with coarse phenocrysts in a finer groundmass) copper deposits, particularly those associated with diorite and granodiorite intrusions.

Alteration

anhydrite and water to gypsum
Ca(SO4) + 2H2O ⇌ Ca(SO4).2H2O
Gypsum is frequently formed by the hydration of anhydrite.

Common impurities: Sr,Ba,H2O

Ankerite

Formula: Ca(Fe2+,Mg)(CO3)2
Forms a series with dolomite and with kutnohorite
Specific gravity: 3.121
Hardness: 3½ to 4
Streak: white
Colour: brown, white to grey, yellowish-brown, greenish
Solubility: Moderately soluble in hydrochloric and sulphuric acid
Environments:

Carbonatites
Hydrothermal environments

Ankerite is a common but not essential constituent of dolostone.

Alteration

ankerite-dolomite and quartz to augite and CO2
Ca(Mg,Fe)(CO3)2 + 2SiO2 → Ca(Mg,Fe)Si2O6 + 2CO2

ankerite-dolomite and quartz to diopside-hedenbergite and CO2
Ca(Fe,Mg)(CO3)2 + 2SiO2 = Ca(Fe,Mg)Si2O6 + 2CO2

calcite, Fe2+ and Mg2+ to ankerite and Ca2+
4CaCO3 + Fe2+ + Mg2+ = 2Ca(Mg0.5Fe0.5)(CO3)2+ 2Ca2+
Ankerite is believed to be formed from calcite hydrothermally according to the above reaction.

Common impurities: Mn

Annite

Formula: KFe2+3(AlSi3O10)(OH)2 phyllosilicate (sheet silicate) mica group
Specific gravity: 3.3
Hardness: 2½ to 3
Streak: Brownish white
Colour: Black, brown
Environments:

Plutonic igneous environments
Metamorphic environments

Annite occurs in igneous and metamorphic rocks that are low in magnesium.

Alteration

almandine and phlogopite to pyrope and annite
Fe2+3Al2(SiO4)3 + KMg3AlSi3O12(OH)2 ⇌ Mg3Al2Si3O12 + KFe3AlSi3O10(OH)2
This assemblage is commonly formed during amphibolite facies metamorphism of pelitic rocks.

sillimanite, annite and H2O to staurolite, muscovite, SiO2 and O2
31Al2SiO5 + 4KFe2+3(AlSi3O10)(OH)2 + 6H2O → 34Fe2+2Al9si4O23(OH) + KAl2 (AlSi3O10)(OH)2 + 7 SiO2 + 1.5O2
Staurolite may occur as a product of retrograde metamorphism according to the above reaction.

staurolite, annite and O2 to hercynite, magnetite, muscovite,corundum, SiO2 and H2O
2Fe2+2Al9Si4O23(OH) + KFe2+3 (AlSi3O10)(OH)2 +2O2 → 4Fe2+Al2O4 + Fe2+Fe3+2O4 + KAl2 (AlSi3O10)OH)2 + 4Al2O3 + 8SiO2 + 2H2O

Common impurities: Ti,Mn,Mg,Ca,Na,K,Cl

Anorthite

Formula: Ca(Al2Si2O8) tectosilicate (framework silicate)
Anorthite is a plagioclase feldspar.
Bytownite is a variety of anorthite
Labradorite is a variety of anorthite
Specific gravity: 2.74 to 2.76, bytownite 2.61 to 2.77
Hardness: 6 to 6½
Streak: White
Colour: Anorthite is colourless, reddish grey or white. Bytownite is colourless, white, greenish, reddish or grey.
Solubility: Anorthite is slightly soluble in hydrochloric acid
Melting point: About 1,550oC at atmospheric pressure
In the continuous branch of the Bowen reaction series anorthite is the first major mineral to crystallise.
Environments (anorthite):

Plutonic igneous environments (labradorite)
Pegmatites (bytownite)
Metamorphic environments

Anorthite is a plagioclase feldspar found in rocks rich in dark minerals, in druses of ejected volcanic blocks and in granular limestone of contact metamorphic deposits. Anorthite also may be found in serpentinite, and hornfels.
Bytownite is found in granite, with hornblende and augite in gabbro, anorthosite, gneiss, granulite, and pegmatites, and lining Alpine cavities and fissures in ore veins.
Labradorite is found with hornblende in basalt, with hornblende and augite in gabbro.
Anorthite is a mineral of the greenschist, amphibolite and granulite facies.

Alteration

aenigmatite, anorthite and O2 to hedenbergite, albite, ilmenite and magnetite
½Na4[Fe2+10Ti2]O4[Si12O36] + CaAl2Si2O8 + ½O2 = CaFe2+Si2O6 + 2NaAlSi3O8 + Fe2+Ti4+O3 + Fe2+Fe3+2O4

Ca-Fe amphibole and anorthite to chlorite, epidote and quartz
CaFe5Al2Si7O22(OH)2 + 3CaAl2Si2O8 + 4H2O → Fe5Al2Si3O10(OH)8 + 2Ca2Al3Si3O12(OH) + 4SiO2

calcium amphibole, calcite and quartz to diopside-hedenbergite, anorthite, CO2 and H2O
Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + 3CaCO3 + 4SiO2 = 3Ca(Fe,Mg)Si2O6 + 2Ca(Al2Si2O8) + 3CO2 + H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

anorthite to calcite and kaolinite in the early Earth's atmosphere
CO2 + H2O + anorthite → calcite + kaolinite
CO2 + 2H2O + CaAl2Si2O8 → CaCO3 + Al2Si2O5(OH)4

anorthite to grossular, kyanite and quartz
3CaAl2 Si2O8 → Ca3Al2(SiO4)3 + 2Al2OSiO4 + SiO2
At 20 kbar pressure the equilibrium temperature is about 1,000oC and at 30 kbar it is about 1,400oC

anorthite and CO2 to meionite (scapolite series), corundum and quartz
4Ca(Al2Si2O8) + CO2 ⇌ Ca4Al6O24(CO3) + Al2O3 + 2SiO2

anorthite, H2O and CO2kaolinite and calcite
2CaAl2 Si2O8 + 4H2O + 2CO2 ⇌ Al4Si4O10(OH)8 + 2CaCO3
calcite is found as a low-temperature, late-stage alteraation product according to the above reaction.

anorthite, H2SO4 and H2O to gypsum and kaolinite
CaAl2 Si2O8 + H2SO4 + 3H2O → CaSO4.2H2O + Al2Si2O5(OH)4

anorthite, albite and H2O to jadeite, lawsonite and quartz
CaAl2 Si2O8 + NaAlSi3O8 + 2H2O → NaAlSi2O6 + CaAl2(Si2O7)(OH)2.H2 + SiO2

anorthite and calcite to meionite (scapolite series)
3Ca(Al2Si2O8) + CaCO3 ⇌ Ca4Al6O24(CO3)
This reaction occurs in the presence of a high CO2 pressure in an environment deficient in (Al+Na+K).

anorthite, enstatite, spinel, K2O and H2O to Al-rich hornblende, Mg-rich sapphirine and phlogopite
2.5Ca(Al2Si2O8) + 10MgSiO3 + 6MgAl2O4 + K2O + 3H2O → Ca2.5Mg4Al(Al2Si6)O22(OH)2 + 3Mg2Al4SiO10 + 2KMg3(AlSi3O10)(OH)2
This reaction occurs in the granulite to amphibolite facies.

calcium amphibole, calcite and quartz to diopside- hedenbergite, anorthite, CO2 and H2O
Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + 3CaCO3 + 4SiO2 = 3Ca(Fe,Mg)Si2O6 + 2Ca(Al2Si2O8) + 3CO2 + H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

calcium amphibole, grossular and quartz to diopside- hedenbergite, anorthite, pyrope-almandine and H2O
2Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + Ca3Al2(SiO4)3 + SiO2 = 3Ca(Fe,Mg)Si2O6 + 4Ca(Al2Si2O8) + (Mg,Fe2+)3Al2(SiO4)3 + 2H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

anorthite variety labradorite, albite, forsterite and diopside to omphacite, garnet and quartz
3CaAl2Si2O8 + 2Na(AlSi3O8) + 3Mg2SiO4 + nCaMgSi2O6 → (2NaAlSi2O6 + nCaMgSi2O6) + 3(CaMg2)Al2(SiO4)3 + 2SiO2
This reaction occurs at high temperature and pressure.

augite, albite, pyroxene, anorthite and ilmenite to omphacite, garnet, quartz and rutile
2MgFe2+Si2O6 + Na(AlSi3O8) + Ca2Mg2Fe2+Fe3+AlSi5O18 + 2Ca(Al2Si2O8) + 2Fe2+Ti4+O3 → NaCa2MgFe2+Al(Si2O6)3 + (Ca2Mg3Fe2+4)(Fe3+Al5)(SiO4)9 + SiO2 + 2TiO2
This reaction occurs at high temperature and pressure.

augite and andalusite to enstatite- ferrosilite and anorthite
Ca(Fe,Mg)Si2O6 + Al2SiO5 → (Mg,Fe2+)SiO3 + Ca(Al2Si2O8)

Fe-rich cordierite and diopside- hedenbergite to enstatite- ferrosilite, anorthite and quartz
(Mg,Fe)2 Al4Si5O18 + 2Ca(Mg,Fe)Si2O6 = 4(Mg,Fe2+)SiO3 + 2Ca(Al2Si2O8) + SiO2

Al-rich enstatite and Al-rich diopside to forsterite, enstatite, diopside and anorthite
Mg9Al2Si9O30 + Ca5Mg4Al2Si9O30 ⇌ 2Mg2SiO4 + 3Mg2Si2O6 + 3CaMgSi2O6 + 2Ca(Al2Si2O8)
This reaction occurs at fairly low temperature and pressure.

enstatite-ferrosilite, diopside-hedenbergite, albite, anorthite and H2O to amphibole and quartz
3(Mg,Fe2+)SiO3 + Ca(Mg,Fe2+)Si2O6 + NaAlSi3O8 + Ca(Al2Si2O8) + H2O ⇌ NaCa2(Mg,Fe)4Al(Al2O6)O22(OH)2 + 4SiO2
This reaction represents metamorphic reactions between the granulite and amphibolite facies.

epidote and chlorite to hornblende and anorthite
6Ca2Al3(SiO4)3(OH) + Mg5Al2Si3O18(OH)8 → Ca2Mg5Si8O22(OH)2 + 10CaAl2Si2O8
This reaction represents changes when the metamorphic grade increases from the greenschist facies to the amphibolite facies.

epidote and quartz to anorthite, grossular and H2O
4Ca2Al3(SiO4)3(OH) + SiO2 → 5CaAl2Si2O8 + Ca3Al2(SiO4)3 + 2H2O
This reaction occurs as the degree of metamorphism increases

forsterite and anorthite to clinoenstatite, diopside and spinel
2Mg2SiO4 + CaAl2Si2O8 ⇌ 2MgSiO3 + CaMgSi2O6 + MgAl2O4

forsterite and anorthite to enstatite, diopside and spinel
2Mg2SiO4 + Ca(Al2Si2O8) = Mg2Si2O6 + CaMgSi2O6 + MgAl2O4

grossular to anorthite, gehlenite and wollastonite
2Ca3Al2(SiO4)3 ⇌ CaAl2Si2O8 + Ca2Al2SiO7 + 3CaSiO3
The equilibrium temperature for this reaction at 5 kbar pressure is 1,110oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

grossular and corundum to anorthite and gehlenite
2Ca3Al2(SiO4)3 + Al2O3 ⇌ CaAl2Si2O8 + Ca2Al2SiO7
The equilibrium temperature for this reaction at 5 kbar pressure is about 950oC At 4.3 kbar pressure the equilibrium temperature is about 890oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

grossular and kyanite to anorthite and corundum
Ca3Al2(SiO4)3 + 3Al2OSiO4 ⇌ 3CaAl2Si2O8 + Al2O3
The equilibrium temperature for this reaction at 10 kbar pressure is about 540oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

grossular, kyanite and quartz to anorthite
Ca3Al2(SiO4)3 + 2Al2OSiO4 + SiO2 ⇌ 3CaAl2Si2O8
The equilibrium temperature for this reaction at 10 kbar pressure is about 510o (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

kyanite to anorthite and corundum
Ca3Al2(SiO4)3 + 3Al2OSiO4 ⇌ 3CaAl2Si2O8 + Al2O3
The equilibrium temperature for this reaction at 10 kbar pressure is about 540oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

grossular, kyanite and quartz to anorthite
Ca3Al2(SiO4)3 + 2Al2OSiO4 + SiO2 ⇌ 3CaAl2Si2O8
The equilibrium temperature for this reaction at 10 kbar pressure is about 510o (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

grossular and quartz to anorthite and wollastonite
Ca3Al2(SiO4)3 + SiO2 ⇌ CaAl2Si2O8 + 2CaSiO3
The equilibrium temperature for this reaction at 5 kbar pressure is 730oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

hornblende, calcite and quartz to Fe-rich diopside, anorthite, CO2 and H2O
Ca2(Mg,Fe2+)3(Al4Si6)O22(OH)2 + 3CaCO3 + 4SiO2 = 3Ca(Mg,Fe2+)Si2O6 + 2Ca(Al2Si2O8) + 3CO2 + H2O
Fe-rich diopside occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies. The above reaction is typical.

hornblende, grossular and quartz to Fe-rich diopside, anorthite, almandine and H2O
2Ca2(Mg,Fe2+)3(Al4Si6)O22(OH)2 + Ca3Al2Si3O12 + 2SiO2 = 3Ca(Mg,Fe2+)Si2O6 + 4CaAl2Si2O8 + (Mg,Fe2+)Al2Si3O12 + 2H2O
Fe-rich diopside occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies. The above reaction is typical.

Al-rich hornblende, spinel, quartz, K2O and H2O to anorthite, Mg-rich sapphirine and phlogopite
Ca2.5Mg4Al(Al2Si6)O22(OH)2 + 4 MgAl2O4 + 6SiO2 + K2O + H2O → 2.5Ca(Al2Si2O8) + Mg2Al4SiO10 + 2KMg3(AlSi3O10)(OH)2

kyanite and zoisite to anorthite, corundum and H2O
2Al2O(SiO4) + 2Ca2Al3[Si2O7][SiO4]O(OH) ⇌ 4CaAl2Si2O8 + Al2O3 + H2O
The equilibrium temperature for this reaction at 5 kbar pressure is 480oC (greenschist facies), and at 10 kbar it is about 720oC (amphibolite facies). The equilibrium is to the right at higher temperatures, and to the left at lower temperatures.

kyanite and zoisite to margarite and anorthite
2Al2O(SiO4) + 2Ca2Al3[Si2O7][SiO4]O(OH) ⇌ CaAl2(Al2Si2O10)(OH)2 + Ca(Al2Si2O8)
The equilibrium temperature for this reaction at 6 kbar pressure is about 520oC (amphibolite facies), and at 9 kbar it is about 675oC (amphibolite facies). At any pressure the euqilibrium is displaced to the right at higher temperatures, and to the left at lower temperatures.

margarite to corundum, anorthite and H2O
CaAl2(Al2Si2O10)(OH)2 ⇌ Al2O3 + Ca(Al2Si2O8)
The equilibrium temperature for this reaction at 6 kbar pressure is about 610oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite and quartz to anorthite, andalusite and H2O
CaAl2(Al2Si2O10)(OH)2 + SiO2 ⇌ Ca(Al2Si2O8) + Al2OSiO4 + H2O
The equilibrium temperature for this reaction at 2 kbar pressure is about 440oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite and quartz to anorthite, kyanite and H2O
CaAl2(Al2Si2O10)(OH)2 + SiO2 ⇌ Ca(Al2Si2O8) + Al2OSiO4 + H2O
The equilibrium temperature for this reaction at 5 kbar pressure is about 520oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

Fe and Cr-rich spinel , diopside and enstatite to forsterite, anorthite and chromite
MgFeAl2Cr2O8 + CaMgSi2O6 + Mg2Si2O6 ⇌ 2Mg2SiO4 + Ca(Al2Si2O8) + Fe2+Cr2O4
This reaction occurs at fairly low temperature and pressure.

zoisite to anorthite, grossular, corundum and H2O
6Ca2Al3[Si2O7][SiO4]O(OH) ⇌ 6CaAl2Si2O8 + 2Ca3Al2Si3O12 + Al2O3 + 3H2O
The equilibrium temperature for this reaction at 6 kbar pressure is about 760oC, and at 10 kbar it is about 950oC (granulite facies). For any given pressure, the reaction goes to the right at higher temperatures, and to the left at lower temperatures.

zoisite and quartz to grossular, anorthite and H2O
4Ca2Al3[Si2O7][SiO4]O(OH) + SiO2 ⇌ Ca3Al2Si3O12 + 5CaAl2Si2O8 + 2H2O
The equilibrium temperature for this reaction at 5 kbar pressure is 650oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

zoisite, kyanite and quartz to anorthite and H2O
2Ca2Al3[Si2O7][SiO4]O(OH) + Al2OSiO4 + SiO2 ⇌ 4Ca(Al2Si2O8) + H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 690oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

zoisite, margarite and quartz to anorthite and H2O
2Ca2Al3[Si2O7][SiO4]O(OH) + CaAl2(Al2Si2O10)(OH)2 + 2SiO2 ⇌ 5Ca(Al2Si2O8) + 2H2O
The equilibrium temperature for this reaction at 6 kbar pressure is about 540oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

Common impurities in anorthite: Ti,Fe,Na,K

Anorthoclase

Anorthoclase is a discredited name for a feldspar intermediate between low sanidine and high albite.

Anthophyllite

Formula: ☐Mg2Mg5Si8O22(OH)2 inosilicate (chain silicate) amphibole
Anthophyllite is a dimorph of cummingtonite. Specific gravity: 2.8 to 3.2
Hardness: 5½
Streak: White
Colour: Brownish, yellowish grey
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Metamorphic environments

Anthophyllite is a metamorphic product of magnesium-rich rocks such as ultramafic igneous rocks and impure dolomite shale. It is common in cordierite-bearing gneiss and schist. It may also form as a retrograde product rimming relict orthopyroxenes such as enstatite, and olivine.
Anthophyllite may be found in gneiss and schist.
It is a mineral of the hornblende-hornfels facies.

Alteration

anthophyllite to enstatite, quartz and H2O
2☐Mg2Mg5Si8O22(OH)2 ⇌ 7Mg2Si2O6 + 2SiO2 + 2H2O
At 10 kbar pressure the equilibrium temperature is about 810oC (granulite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures.

anthophyllite and forsterite to enstatite and H2O
2☐Mg2Mg5Si8O22(OH)2 + 2Mg2SiO4 ⇌ 9Mg2Si2O6 + 2H2O
At 2 kbar pressure the equilibrium temperature is about 690oC (pyroxene-hornfels facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures.

forsterite and talc to anthophyllite and H2O
4Mg2SiO4 + 9Mg3Si4O10(OH)2 ⇌ 5Mg2Mg5Si8O22(OH)2 + 4H2O
At 2 kbar pressure the equilibrium temperature is about 650oC (pyroxene-hornfels facies), with equilibrium to the right at higher temperatures and to the left at lower temperatures (for the same pressure).

talc to anthophyllite, quartz and H2O
7Mg3Si4O10(OH)2 ⇌ 3☐Mg2Mg5Si8O22(OH)2 + 4SiO2 + 4H2O
At 10 kbar pressure the equilibrium temperature is about 790oC (granulite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures.

talc and enstatite to anthophyllite
Mg3Si4O10(OH)2 + 2Mg2Si2O6 → ☐Mg2Mg5Si8O22(OH)2
At 10 kbar pressure the equilibrium temperature is 750oC granulite facies.

Common impurities: Ti,Al,Mn,Ca,Na

Antigorite

Formula: Mg3Si2O5(OH)4 phyllosilicate (sheet silicate), serpentine group
Specific gravity: 2.0 to 2.6
Hardness: 2½ to 4
Streak: White
Colour: Green, grey to black, white, brownish
Solubility: Insoluble in water, nitric and sulphuric acid; soluble in hydrochloric acid
Environments:

Metamorphic environments

Antigorite forms in reactions at temperatures that can exceed 600°C during metamorphism, and it is the serpentine group mineral stable at the highest temperatures. It is common in regional and contact metamorphosed serpentinite.
It is a mineral of the blueschist and greenschist facies.

Alteration

antigorite to forsterite, talc and H2O
5Mg3Si2O5(OH)4 = 6Mg2SiO4 + Mg3Si4O10(OH)2 + 9H2O
This reaction may occur in olivine-diopside- antigorite schist within the aureole of the tonalite in the southern Bergell Alps, Italy, at a higher grade of metamorphism than that which produces forsterite and tremolite.
At 10 kbar pressure the equilibrium temperature is about 600oC (amphibolite facies), with equilibrium to the right at higher temperatures and to the left at lower temperatures (for the same pressure).

antigorite and calcite to forsterite, diopside, CO2 and H2O
3Mg3Si2O5(OH)4 + CaCO3 → 4Mg2SiO4 + CaMgSi2O6 + CO2 +6 H2O
This reaction has been found to occur in antigorite schist. At at about 3 kbar pressure and 400 to 500oC (greenschist facies).

antigorite and magnesite to forsterite, CO2 and H2O
Mg3Si2O5(OH)4 + MgCO3 → 2Mg2SiO4 + CO2 + 2H2O

antigorite and muscovite to phlogopite, amesite, SiO2 and H2O
5Mg3Si2O5(OH)4 + 3KAl2(AlSi3O10)(OH)2 → 3KMg3(AlSi3O10)(OH)2 + 3Mg2Al(AlSiO5)(OH)4 + 7SiO2 + 4H2O

brucite and antigorite to forsterite and H2O
Mg(OH)2 + Mg3Si2O5(OH)4 ⇌ 2Mg2SiO4 + 3H2O
The equilibrium temperature for this reaction at 8 kbar pressure is about 450oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures. The reaction also may occur in the albite-epidote-hornfels and blueschist facies.

diopside and antigorite to forsterite, Mg-rich tremolite and H2O
2CaMgSi2O6 + 5Mg3Si2O5(OH)4 ⇌ 6Mg2SIO4 + Ca2Mg5Si8O22(OH)2 + 9H2O
At 10 kbar pressure the equilibrium temperature is about 580oC (amphibolite facies).

See also results for serpentine, which is a group of minerals including antigorite, chrysotile and lizardite, all of which share the same formula, although they have slightly different structures.

Common impurities: Ni,Al,Mn

Antlerite

Formula: Cu2+3(SO4)(OH)4 anhydrous sulphate containing hydroxyl
Pseudomorphs of cuprite after fibrous antlerite have been observed
Specific gravity: 3.9
Hardness: 3½
Streak: Light green
Colour: Emerald-green to blackish-green, also light green
Solubility: Soluble in dilute sulphuric acid
Environments:

Hydrothermal environments

Antlerite is a secondary mineral occurring in the oxidised zone of copper deposits in arid regions.
It is metastable at ambient temperature with respect to brochantite.

Apachite

Formula: Cu2+9Si10O29.11H2O unclassified silicate
Specific gravity: 2.80
Hardness: 2
Colour: Blue
Environments:

Metamorphic environments
Hydrothermal environments

Apachite is a retrograde metamorphic or mixed hypogene and supergene mineral formed at the expense of a prograde (increasing metamorphic grade) calc-silicate and sulphide assemblage in metamorphosed carbonate rocks. At the type locality, the Christmas mine, Gila County, USA, it is typically found in fractured zones cutting garnet-diopside rock, replacing both these silcates and calcite. Associated minerals are kinoite, gilalite, stringhamite, junitoite, clinohedrite, xonotlite, calcite and tobermorite.

Common impurities: Mg,Ca

Apatite

The apatite group comprises three minerals:
Fluorapatite: Ca5(PO4)3F
Hydroxylapatite: Ca5(PO4)3(OH)
Chlorapatite: Ca5(PO4)3Cl
All of these are anhydrous phosphates containing hydroxyl or halogen
Fluorapatite is the commonest mineral in the apatite group.
Properties of fluorapatite:
Specific gravity: 3.1 to 3.25
Hardness: 5
Streak: White
Colour: Colourless, yellow, green, blue and purple. Manganoan varieties are dark green and blue-green.
Solubility: Apatite is slightly soluble in sulphuric acid and moderately soluble in hydrochloric and nitric acid
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Apatite is a primary and secondary mineral, widely distributed with important concentrations in carbonatites. It is the most common rock-forming phosphate and a major mineral in lithified phosphate-rich sediments. It occurs the oxidation zone of hypothermal (high temperature) veins and in Alpine cleft-type veins.
It is a common secondary mineral in high-temperature alteration zones.
Apatite is a common constituent of marble, skarn and magnetite deposits.
Apatite may also be found in quartzolite, granite, syenite, diorite, rhyolite, trachyte, andesite and basalt.

Common impurities: OH,Cl,transition elements,La,Ce,Pr,Nd,Sm,Eu,Gd,Dy,Y,Er,Mn

Aphthitalite

Formula: K3Na(SO4)2 anhydrous normal sulphate
Specific gravity: 2.66 to 2.71
Hardness: 3
Streak: White
Colour: Colourless (rare), white, grey, bluish, greenish, reddish; colourless in transmitted light
Solubility: Soluble in water
Environments:

Sedimentary environments
Fumeroles

Aphthitalite occurs in two different environments. It is formed in volcanoes as incrustations in fumeroles, where it may deposit from volcanic gas during cooling from about 800 down to 400oC, together with thénardite. It also occurs in lacustrine (lake) salt deposits.

Apophyllite

Apophyllite refers to a three minerals:
Fluorapophyllite-(K) KCa4Si8O20F.8H2O
Fluorapophyllite-(Na) NaCa4Si8O20F.8H2O and
Hydroxyapophyllite-(K) KCa4Si8O20(OH,F).8H2O
They are all phyllosilicates (sheet silicates)
Specific gravity: 2.3 to 2.4
Hardness: 4½ to 5
Streak: White
Colour: Colourless, white, yellow, green, brown, pink
Solubility: Moderately soluble in hydrochloric acid
Environments:

Basaltic cavities

Apophyllite occurs as a secondary mineral lining cavities in basalt and related rocks, associated with zeolites, calcite, datolite and pectolite.

Aragonite

Formula: Ca(CO3) carbonate
Specific gravity: 2.947
Hardness: 3½ to 4
Streak: White
Colour: colourless to white or grey, often stained blue, green, red or violet by impurities; colourless in transmitted light.
Solubility: Readily soluble in hydrochloric, sulphuric and nitric acid
Environments:

Sedimentary environments
Hot spring deposits
Hydrothermal environments

Aragonite is found in the oxidised zones of ore deposits and in evaporites, hot spring deposits and limestone caves. It is also found in some metamorphic and igneous rocks. It occurs with siderite in iron deposits and with calcite, dolomite and other magnesium minerals in altered serpentinite, dunite and peridotite.
Aragonite is a common constituent of limestone.
It is a mineral of the blueschist facies where it may be associated with glaucophane.

Alteration

Aragonite and calcite are both forms of calcium carbonate. Aragonite is less stable than calcite under atmospheric conditions, but the alteration of aragonite to calcite is a very slow reaction, so calcite and aragonite can co-exist in new rocks, but aragonite is a rare mineral in old rocks and shells. At extremely high pressure aragonite is the stable mineral.

Calcite and aragonite are precipitated according to the following reactions:
Carbon dioxide in the atmosphere is dissolved in rainwater forming weak carbonic acid:
H2O + CO2 → H2CO3
Carbonic acid dissolves limestone forming calcium bicarbonate
H2CO3 + CaCO3 → Ca(HCO3)2
This solution percolates into caves where calcium carbonate may be precipitated with the release of liquid water and gaseous carbon dioxide:
Ca(HCO3)2 ⇆ CaCO3 (solid) + H2O (liquid) + CO2 (gas)
The net effect of these changes could be written as the reversible reaction
CaCO3 (solid) + H2CO3 (in solution) ⇌ Ca2+ + 2(HCO3)-
The forward reaction, solution of calcium carbonate, occurs in acid environments, and the reverse reaction, precipitation of calcium carbonate, occurs in strongly basic (alkaline) environments.

Common impurities: Sr,Pb,Zn

Arseniosiderite

Formula: Ca2Fe3+3O2(AsO4)3.3H2O hydrated arsenate containing hydroxyl
Forms pseudomorphs after siderite and scorodite
Specific gravity: 3.60
Hardness: 4½, 1½ in fibres
Streak: ochre-yellow
Colour: Golden-yellow to yellow-brown, reddish-brown, brown, black; reddish brown to brownish yellow in transmitted light
Solubility: Readily soluble in hot acids
Environments:

Hydrothermal environments

Arseniosiderite is a rare secondary mineral formed by the low-temperature oxidation of earlier arsenic-bearing minerals, such as scorodite, arsenopyrite and löllingite. Associated Minerals at the type locality include quartz, psilomelane, hematite and goethite.

Localities

Austria

At Hūttenberg, Carinthia, arseniosiderite occurs in felted masses with scorodite, symplesite, pitticite and pharmacolite on löllingite.

France

At Romanêche-Thorins, Saône et Loire, in a manganese deposit with quartz, goethite, romanèchite and psilomelane.

Germany

At Schneeberg, Bavaria, arseniosiderite occurs with erythrite and roselite.

Mexico

At the Jesus Maria Mine, Mazapil district, arseniosiderite occurs with pharmacolite, chrysocolla and calcite, and as pseudomorphs after scorodite.

Arsenopyrite

Formula: FeAsS supharsenide
Specific gravity: 5.9 - 6.2
Hardness: 5½ - 6
Streak: Black
Colour: Tin white to steel white
Solubility: Arsenopyrite is moderately soluble in nitric acid but insoluble in hydrochloric and sulphuric acids
Environments:

Pegmatites (sparingly)
Hydrothermal environments

Arsenopyrite is the most common arsenic-containing mineral. It occurs with tin and tungsten ores in high-temperature hydrothermal deposits, associated with silver and copper ores, galena, sphalerite, pyrite and chalcopyrite. It is frequently associated with gold. It is found in contact metamorphic deposits, and disseminated in limestone.

Common impurities: Ag,Au,Co,Sn,Ni,Sb,Bi,Cu,Pb

Augite

Formula: (Ca,Mg,Fe)2Si2O6 Inosilicate (chain silicate), pyroxene group
Specific gravity: 3.19 to 3.56
Hardness: 5½ to 6
Streak: Greenish gray, light to dark brown
Colour: Black, brown, green
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments:

Plutonic igneous environments (typical)
Pegmatites
Carbonatites
Metamorphic environments

Augite is a primary and secondary mineral and it is the most common pyroxene. It is an important rock-forming mineral, found chiefly in dark coloured igneous rocks. The melting point of pyroxenes is about 1,000oC.

Augite is a common but not essential constituent of gabbro, anorthosite, peridotite, kimberlite, rhyolite, trachyte, andesite and basalt.
It also may be found in granite.

Alteration

ankerite, dolomite and quartz to augite and CO2
Ca(Mg,Fe)(CO3)2 + 2SiO2 → Ca(Mg,Fe)Si2O6 + 2CO2

augite and CO2 to hypersthene, calcite and quartz
Ca(Mg,Fe)Si2O6 + CO2 → (Mg,Fe)SiO3 + CaCO3 + SiO2

augite, albite, pyroxene, anorthite and ilmenite to omphacite, garnet, quartz and rutile
2MgFe2+Si2O6 + Na(AlSi3O8) + Ca2Mg2Fe2+Fe3+AlSi5O18 + 2Ca(Al2Si2O8) + 2Fe2+Ti4+O3 → NaCa2MgFe2+Al(Si2O6)3 + (Ca2Mg3Fe2+4)(Fe3+Al5)(SiO4)9 + SiO2 + 2TiO2
This reaction occurs at high temperature and pressure.

augite and andalusite to enstatite- ferrosilite and anorthite
Ca(Fe,Mg)Si2O6 +Al2SiO5 → (Mg,Fe2+)SiO3 + Ca(Al2Si2O8)

Fe-rich dolomite and quartz to augite and CO2
Ca(Mg,Fe)(CO3)2 + 2SiO2 → Ca(Mg,Fe)Si2O6 + 2CO2

hypersthene, augite and Fe and Cr-rich spinel to garnet and olivine
2(Mg,Fe)SiO3 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4

meionite (scapolite series) and augite to garnet, calcite and quartz
Ca4Al6O24(CO3) + 3Ca(Mg,Fe2+)Si2O6 ⇌ 3Ca2(Mg,Fe2+)Al2(SiO4)3 + CaCO3 + 3SiO2

Common impurities: Ti,Cr,Na,Mn,K

Aurichalcite

Formula: (Zn,Cu)5(CO3)2(OH)6 carbonate
Specific gravity: 3.6 to 4.3
Hardness: 2
Streak: White to light blue
Colour: Light blue, bluish and greenish blue
Solubility: Moderately soluble in hydrochloric, sulphuric and nitric acid
Environments:

Hydrothermal environments

Aurichalcite is a secondary mineral occuring in the oxidation zone of hypothermal (high temperature) veins in copper and zinc deposits.

Common impurities: Ca

Autunite

Formula: Ca(UO2)2(PO4)2.10-12H2 hydrated normal phosphate
Specific gravity: 3.2
Hardness: 2 to 2½
Streak: White to yellowish
Colour: Yellow, due to the uranyl ion UO2+2
Solubility: Autunite is moderately soluble in hydrochloric, sulphuric and nitric acid
Environments:

Hydrothermal environments

Autunite is a secondary mineral found chiefly in the zone of oxidation and weathering derived from the alteration of uraninite or other uranium minerals in hypothermal (high temperature) veins.

Common impurities: Ba,Mg

Axinite

Axinite represents three minerals:
Axinite-(Fe) Ca2(Fe2+Al2BSi4O15(OH)
Axinite-(Mg) Ca2MgAl2BSi4O15(OH) and
Axinite-(Mn) Ca2(Mn2+Al2BSi4O15(OH)
All of these are sorosilicates (Si2O7 groups) with additional (OH) Specific gravity: 3.3
Hardness: 6½ to 7
Streak: White
Colour: Brown, grey, violet, blue, greenish
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments:

Plutonic igneous environments
Pegmatites
Metamorphic environments

Axinite occurs in cavities in granite, in pegmatites, and in the contact zones surrounding granitic intrusions.

Common impurities for Axinite-(Mg): Ti,V,Mn,Zn,K,H2O;
Common impurities for Axinite-(Mn): Ti,Fe,Mg,Na,K, H2O

Azurite

Formula: Cu3(CO3)2(OH)2 anhydrous carbonate containing hydroxyl
Specific gravity: 3.77
Hardness: 3½ to 4
Streak: Light blue
Colour: Deep blue
Solubility: Azurite is moderately soluble in hydrochloric, sulphuric and nitric acid
Environments:

Carbonatites
Hydrothermal environments

Azurite is less common than malachite but has the same origin and associations. It is a secondary mineral found largely in the oxidation portions of high temperature copper deposits.

It may be found in gneiss.

Alteration

Azurite is formed by the action of carbonated water on copper-containing minerals, or from copper-containing solutions, such as CuSO4 or CuCl2 reacting with limestone.

azurite and H2O to malachite and CO2
2Cu3(CO3)2(OH)2 + H2O → 3Cu2(CO3(OH)2 + CO2
Azurite is unstable under atmospheric conditions, and slowly converts to the more stable malachite according to the above reaction.

Bariopharmacosiderite

Formula: Ba0.5Fe3+4(AsO4)3(OH)4.5H2O

Baryte

Formula: Ba(SO4) sulphate
Specific gravity: 4.48
Hardness: 3 to 3½
Streak: White
Colour: Colourless, white, yellowish, reddish, blue
Solubility: Insoluble in water, hydrochloric and nitric acid; soluble in sulphuric acid if heated
Environments:

Carbonatites (typical)
Sedimentary environments
Hydrothermal environments (typical)

Baryte is a common and widely distributed mineral. It is a typical mineral in epithermal (low temperature) and mesothermal hydrothermal veins in metamorphic rocks and in limestone with calcite and associated with ores of silver, lead, copper, cobalt, manganese and antimony. It is also found as residual masses in clay overlying limestone. Also as concretions in sandstone. and other sedimentary rocks. In places acts as a cement in sandstone but it may also be found as lenses or replacement deposits in sedimentary rocks, both of primary and secondary origin.
Baryte precipitates with decreasing temperature from oxidised fluids with moderate salinities over a temperature range up to 300oC. At low salinities baryte becomes more soluble (retrograde solubility) above about 100oC.

Alteration

calcite, Ba2+, H2S and O2 to baryte, Ca2+, CO2 and H2O
CaCO3 + Ba2+ + H2S + 2O2 = BaSO4 + Ca2+ + CO2 and H2O
Baryte may be precipitated by the action of ore fluid and groundwater on calcite.

Localities

Iran

At Mount Kahoven, Semnan Province, snow white crystals of baryte are found on quartz coloured deep red by hematite. The lack of hematite staining the baryte shows that it, the baryte, was formed later than the quartz.

Bastnäsite

Formula:
Bastnäsite-(Ce): Ce(CO3)F the most common member of the bastnäsite group
Bastnäsite-(La): La(CO3)F
Bastnäsite-(Nd): Nd(CO3)F
Bastnäsite-(Y): Y(CO3)F
All of these are anhydrous carbonates containing halogen
Bastnäsite forms oriented overgrowths and alteration pseudomorphs after fluocerite. Crystal axes of both species oriented in parallel position
Specific gravity: 4.9 to 5.2
Hardness: 4 to 5
Streak: White
Colour: Yellow, reddish-brown; colourless to light yellow in transmitted light; bastnäsite-(Nd) may be pale purplish pink to colourless
Solubility: Bastnäsite-(Ce) is soluble in strong, hot acids
Environments:

Pegmatites
Metamorphic environments

Bastnäsite-(Ce) occurs in contact metamorphic amphibole skarn; bastnäsite-(Nd) occurs in the outer rim zone in crystals of bastnäsite-(Ce), found in cavities in yttrian fluorite, and in granite pegmatites

Bauxite

Bauxite is not a mineral, but a mixture of iron and aluminium oxides and hydroxides which is the principal ore of aluminium. It is almost always a residual soil rather than a sediment. Major constituents are gibbsite, böhmite and diaspore.

Bayldonite

Formula: Cu3PbO(AsO3OH)2(OH)2
Specific gravity: 5.5
Hardness: 4½
Streak: Siskin green to apple green
Colour: Green, apple-green, yellow-green
Solubility: Soluble with difficulty in hydrochloric acid

Hydrothermal environments

Occurrence: Bayldonite is a relatively rare secondary mineral occurring in the oxidised zones of polymetallic deposits.

Beryl

Formula: Be3Al2Si6O18 cyclosilicate (ring silicate)
Specific gravity: 2.63 to 2.92
Hardness: 7½ to 8
Streak: White
Colour: Pure beryl is colourless, but it occurs in many different colours due to impurities. Goshenite is the colourless, gemmy variety of beryl. The blue-green colour of aquamarine is caused by trivalent iron Fe3+ and divalent iron Fe2+ in different positions in the crystal lattice. The golden yellow colour of heliodor is caused by trivalent iron Fe3+; the green of emerald is caused by chromium and/or vanadium; the pink of morganite is caused by small amounts of manganese and the deep red of red beryl is also caused by trivalent manganese Mn3+.
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Plutonic igneous environments
Pegmatites (typical)
Metamorphic environments

Beryl, although containing the rare element Be, is rather common and widely distributed. It occurs usually in granitic rocks, or in pegmatites. It is also found in mica schist of regional metamorphic rocks.

In pegmatites, associations include quartz, microcline, albite, muscovite, biotite, members of the columbite-tantalite series, cookeite (Al,Li)3Al2(Si,Al)4OSub>10(OH)8, tourmaline, lepidolite, topaz and spessartine.
In medium-temperature metamorphic deposits beryl is associated with topaz, cassiterite and ferberite- hübnerite MnWO4;
in Alpine and hydrothermal veins it is found with quartz and feldspar.

Red beryl is found in topaz rhyolites with topaz, high-temperature quartz and bixbyite Mn3+2O3.

Alteration

At high temperature and pressure beryl commonly alters to different secondary minerals, depending on the pH.
At pH 2 to 3 (strongly acid) quartz is the dominant alteration product.
At pH 4 to 5 bertrandite Be4Si2O7(OH)2, euclase BeAlSiO4(OH) or phenakite are formed.
Near the neutral pH of 7 bertrandite Be4Si2O7(OH)2 or bavenite Ca4Be2+xAl2-xSi9O26-x(OH)2+x, with x between 0 and 1, are produced.
At pH of 8 to 9 (alkaline) bavenite, milarite KCa2(Be2AlSi12)O30.H2O (not to be confused with millerite) or bityite CaLiAl2(Si2BeAl)O10(OH)2 are produced.
At pH 10 to 11 (strongly alkaline) epididymite or eudidymite, both Na2Be2Si6O15.H2O, are produced.
At high temperature and pressure beryl becomes unstable and breaks down into chrysoberyl, phenakite and quartz.

Common impurities: Fe,Mn,Mg,Ca,Cr,Na,Li,Cs,O,H,OH,H2O,K,Rb

Localities

Australia

At Tom's quarry, South Australia, beryl occurs intergrown with childrenite Fe2+Al(PO4)(OH)2.H2O, variscite Al(PO4).2H2O and strontium and iron bearing crandallite.

Canada

At Airy Creek, British Columbia, aquamarine (a variety of beryl) occurs in a granite pegmatite dyke that cuts high-grade metamorphic gneiss.

At Lened, Tungsten, Northwest Territories, Canada, emerald (a variety of beryl) occurs in a series of vuggy quartz/carbonate veins within a calc-silicate skarn. The colour is probably due to traces of vanadium.

At the Little Nahanni Pegmatite Group, Tungsten, Northwest Territories, Canada, goshenite (a variety of beryl) occurs within a series of lithium-bearing pegmatites.

At Mountain River, Mackenzie Mountains, Northwest Territories, Canada, emerald occurs in quartz-plagioclase-carbonate veins hosted in shale, siltstone and sandstone. The colour is due to chromium Cr and vanadium V.

At Port Joli, Nova Scotia, Canada, beryl occurs embedded in pegmatite within a biotite granite.

The Taylor pegmatite, Ontario, Canada, intrudes altered ultramafic rocks, which are the likely source of chromium which causes the green colour of the emerald which is found there.

China

At Pingwu County, Sichuan, China, beryl is associated with tin and tungsten minerals.

USA

In New York City beryl crystals are found in pegmatites that cut schist and gneiss, and also frozen in a smoky quartz matrix.

The consolidated Quarry at Maine, USA, is in a simple granite pegmatite, enriched in lithium in some zones. These have cavities that contain albite, muscovite and beryl, together with other minerals. The paragenesis for the beryl alteration is
beryl → beryllonite NaBe(PO4) → moraesite Be2(PO4) (OH).4H2O → hydroxylherderite CaBe(PO4)(OH) → fluorapatite → greifensteinite Ca2Be4Fe2+5(PO4)6(OH)4.6H2O.
Late-stage low-temperature aqueous fluids likely caused partial dissolution of primary beryl resulting in the formation of hydroxylherderite and other secondary beryllium phosphates.

At Yucca Valley, California, aquamarine occurs in pockets in pegmatite associated with cleavelandite and smoky quartz.

In the Sierrita Mountains, Arizona, aquamarine occurs in pegmatites embedded in white quartz enclosed by feldspar, with quartz and mica or in contact with biotite.

At Stoneham, Maine, beryl occurs mostly in solid pegmatites, and only rarely in pockets. When it is in quartz it is aquamarine, but the beryl occurring in feldspar is common beryl.

Beudantite

Formula: PbFe3+3(AsO4)(SO4)(OH)6 compound arsenate
Beudantite Group > Alunite Supergroup
Specific gravity: 4.48
Hardness: 3½ to 4½
Streak: Black to grey
Colour: Dark green, brown, black
Solubility: Soluble in HCl.

Hydrothermal environments

Beudantite is a secondary mineral occurring in the oxidised zones of polymetallic deposits. Some beudantite may contain minor antimony Sb replacing iron Fe.

Localities

Germany

At the Clara Mine, in the Black Forest, beudantite is common, lining cavities in baryte or quartz, and associated with segnitite, kintoreite, corkite and dussertite.

United Kingdom

At Burdell Gill, Cumbria, beudantite is uncommon, but it sometimes occurs on baryte or quartz associated with mimetite and carminite.

At Roughton Gill, Cumbria, beudantite occurs as crusts on quartz, and also in cellular quartz veinstone, with baryte and lepidocrocite. It is sometimes associated with carminite.

At Sandbed, Cumbria, beudantitee occurs as a encrustation on mimetite with scorodite and pharmacosiderite. A mineral intermediate between beudantite and segnitite occurs in cavities in quartz, apparantly formed by the oxidation of primary arsenopyrite.

At Short Grain, Cumbria, beudantite occurs on quartz or baryte associated with mimetite, arseniosiderite and carminite. It sometimes forms pseudomorphs after mimetite. Other associates include a href="#primary and secondary"target="_self">supergene baryte and bariopharmacosiderite.

At Silver Gill, Cumbria, beudantite occurs coating mimetite crystals.

USA

At the San Rafael Mine, Nevada, beudantite occurs in boxwork limonite associated with segnitite, mimetite and adamite, and also within quartz-lined vugs.

Common impurities: Al,P

Biotite

Biotite refers to dark mica minerals, such as manganophyllite and phlogopite KMg3(AlSi3O10)(OH)2 phyllosilicate (sheet silicate)
In the discontinuous branch of the Bowen reaction series biotite is intermediate between amphibole (higher temperature) and orthoclase (lower temperature, after joining with the continuous branch).
Environments:

Plutonic igneous environments (typical)
Volcanic igneous environments
Pegmatites
Metamorphic environments
Hydrothermal environments

Solubility: Slightly soluble in sulphuric acid

In metamorphic environments biotite is formed over a wide range of temperature and pressure conditions, in both regionally metamorphosed and contact metamorphosed rocks.
Typical associations are biotite with chlorite and biotite with muscovite.
Biotite is a primary and secondary mineral.
It is an essential constituent of phyllite.
It is a common constituent of granite, diorite, rhyolite, andesite schist and gneiss.
It also may be found in norite, syenite, gabbro, trachyte, basalt, limestone, dolostone and hornfels.
Biotite is characteristic of the greenschist facies and it is also a mineral of the albite-epidote-hornfels, hornblende-hornfels, pyroxene-hornfels and amphibolite facies.
It never occurs in the sanidinite facies

Alteration

Biotite is a significant hydrothermal mineral that commonly replaces ferromagnesian minerals.

biotite and quartz to enstatite- ferrosilite, orthoclase and H2O
K(Mg,Fe)3(AlSi3O10)(OH)2 + 3SiO2 → 3(Mg,Fe2+)SiO3 + KAlSi3O8 + H2O
enstatite-ferrosilite may develop from the breakdown of biotite according to the above reaction.

chlorite, muscovite and quartz to biotite, Fe-rich cordierite and H2O
(Mg,Fe2+)5Al(AlSi3O10)(OH)8 + KAl2(AlSi3O10)(OH)2 + 2SiO2 → K(Mg,Fe2+)3(AlSi3O10)(OH)2 + (Mg,Fe2+)2Al4Si5O18 + 4H2O
This reaction ocurs when the metamorphic grade increases

enstatite-ferrosilite, K-feldspar and H2O to biotite and quartz
3(Mg,Fe2+)SiO3 + K(AlSi3O8) + H2O ⇌ K(Mg,Fe)3(AlSi3O10)(OH)2+ 3SiO2
The forward reaction leads to an amphibolite facies assemblage.

muscovite, biotite and SiO2 to K-feldspar, garnet and H2O
KAl2(AlSi3O10)(OH)2 + K(Fe2+,Mg)3(AlSi3O10)(OH)2 + 3SiO2 → 2KAlSi3O8 + (Fe2+,Mg)3Al2(SiO4)3 + 2H2O

muscovite and garnet to biotite, sillimanite and quartz
KAl2(AlSi3O10)(OH)2 + (Fe2+,Mg)3Al2(SiO4)3 → K(Fe2+,Mg)3(AlSi3O10)(OH)2 + 2Al2SiO5 + SiO2
Muscovite is unstable in combination with garnet.

Bismuth

Formula: Bi native element
Specific gravity: 9.7 - 9.8
Hardness: 2 to 2½
Streak: Lead grey
Colour: Silver white
Solubility: Slightly soluble in hydrochloric acid, readily soluble in sulphuric and nitric acid
Environments:

Pegmatites
hydrothermal environments
Hydrothermal environments

Bismuth occurs in pegmatites and as an unaltered primary mineral in hypothermal, (high temperature) tin ore veins.

Common impurities: Fe,Te,As,S,Sb

Bismuthinite

Formula: Bi2S3 sulphide
Specific gravity: 6.8 to 7.2
Hardness: 2
Streak: Grey
Colour: Lead grey to yellowish white
Solubility: Insoluble in hydrochloric acid and sulphuric acid; readily soluble in nitric acid
Environments:

Pegmatites
Metamorphic environments
Hydrothermal environments

Bismuthinite occurs as an unaltered primary mineral in hypothermal (high temperature) hydrothermal veins in tin and silver-cobalt deposits, and more rarely in contact metamorphic deposits and pegmatites.

Common impurities: Pb,Cu,Fe,As,Sb,Se,Te

Bixbyite

Formula: Mn3+2O3 simple oxide
Specific gravity: 4.945
Hardness: 6 to 6½
Streak: Black
Colour: Black
Environments:

Volcanic igneous environments
Metamorphic environments
Hydrothermal environments

Alteration

hausmannite and O2 to bixbyite
4Mn2+Mn3+2O4 + O2 ⇌ 6Mn2O3

rhodochrosite and O2 to bixbyite and CO2
4MnCO3 + O2 ⇌ 2Mn3+2O3 +4CO2
A higher temperature favours the forward reaction

Common impurities: Al,Mg,Si,Ti

Localities

Sweden

At Långban bixbyite occurs in metamorphosed manganese ores.

USA

At the Black Range tin district, New Mexico, it occurs in rhyolite.

At Topaz Mountain, Utah, bixbyite occurs in cavities in rhyolite associated with topaz, spessartine, red beryl and hematite, also with fluorite.

Böhmite

Formula: AlO(OH) oxide containing hydroxyl
Specific gravity: 3.03
Hardness: 3½
Streak: White
Colour: White to grey
Environments:

Pegmatites
Metamorphic environments

Böhmite is widely distributed in bauxite. It also may exsolve from corundum.

Borax

Formula: Na2B4O5(OH)4.8H2O hydrated borate containing hydroxyl
Specific gravity: 1.7 - 1.8
Hardness: 2 to 2½
Streak: White
Colour: White, yellowish, seldom bluish, greenish
Solubility: Soluble in water.
Melting point: 878 °C. The melt dissolves numerous metal oxides. Loses 5 mol of water when heated to 100°C, another 4 mol when heated to 150 °C, and the last mol at 400 °C. Rapidly dehydrates in air to tincalconite.
Environments:

Sedimentary environments (typical)
Volcanic sublimates and hot spring deposits

Borax is the most widespread of the borate minerals. It is formed by evaporation of enclosed lakes and as an efflorescence on the surface in arid regions. It occurs in salt lake beds, hot spring deposits and volcanic vents.

Bornite

Formula: Cu5FeS4 sulphide
Specific gravity:4.9 to 5.3
Hardness: 3
Streak: Dark grey
Colour: Reddish silver grey on fresh break
Solubility: Moderately soluble in nitric acid
Environments:

Pegmatites
Carbonatites
Metamorphic environments
Hydrothermal environments

Bornite is a widely occurring copper ore usually found associated with chalcocite, chalcopyrite, covellite, pyrrhotite, pyrite and other sulphides, especially in the enriched zone of mesothermal (moderate temperature) and hypothermal (high temperature) veins. It is less frequently found as secondary deposits in the oxidation zone of copper veins. It occurs disseminated in ultramafic rocks, in contact and regional metamorphic deposits and in pegmatites.

Alteration

Chalcopyrite CuFeS2 (primary) readily alters to the secondary minerals bornite, covellite and brochantite.

chalcopyrite and chalcocite to bornite
CuFe3+S2 + 2Cu2S = Cu5FeS4

Common impurities: Ag,Ge,Bi,In,Pb

Bournonite

Formula: CuPbSbS3 sulphosalt
Bournonite-Seligmannite Series.
Specific gravity: 5.83
Hardness: 2½ to 3
Streak: Steel grey
Colour: Steel grey
Solubility: Slightly soluble in nitric acid
Environments:

Hydrothermal environments

Bournonite is found in mesothermal veins, both as a primary mineral and in the enriched zone

Boulangerite

Formula: Pb5Sb4S11 sulfosalt
Specific gravity: 6.0 to 6.3
Hardness: 2½ to 3
Streak: Brown to brown-grey
Colour: Lead-grey
Environments:

Hydrothermal environments

Boulangerite occurs in low to moderate temperature hydrothermal veins, associated with lead sulfosalts, galena, stibnite, sphalerite, pyrite, arsenopyrite, siderite and quartz.
Common impurities: Cu,Zn,Sn,Fe

Bradleyite

Formula: Na3Mg(PO4)(CO3) compound phosphate
Specific gravity: 2.734
Hardness: 3 to 4
Streak: White
Colour: Light grey
Solubility: Slowly decomposed by cold water; readily soluble in dilute hydrochloric acid
Environments:

Sedimentary environments

Bradleyite is a rare mineral in oil shale deposits of the Green River formation in Colorado, Wyoming and Utah, USA.

Braunite

Formula: Mn2+Mn3+6O8(SiO4) multiple oxide
Specific gravity: 4.75
Hardness: 6 to 6½
Streak: Black
Colour: Black
Environments:

Sedimentary environments
Metamorphic environments
Hydrothermal environments

Braunite is formed by metamorphism of manganese silicates and oxides, or as a product of weathering. Associated minerals are pyrolusite, jacobsite, hausmannite, bixbyite, rhodonite, spessartine and hematite. Braunite from arenaceous beds on the farm Weenen, Northern Transvaal, South Africa, occurs in low grade ore of a sedimentary origin with supergene enrichment. Other manganese minerals in this ore are psilomelane, and pyrolusite.

Braunite is both an ore-forming mineral and a precursor of supergene oxide ores in manganese deposits worldwide. It is essentially of sedimentary origin. Braunite assemblages are found in rocks of all metamorphic grades:

Greenschist facies, biotite grade: either pyrolusite, braunite and quartz or braunite, bixbyite and quartz

Amphibolite facies facies, garnet and staurolite-kyanite grades: braunite, rhodonite and quartz

Granulite facies, sillimanite grade: either braunite, bixbyite and quartz or braunite, rhodonite and quartz

Progressively higher temperatures resulted in braunite coexisting with more reduced manganese oxides and ultimately with rhodonite or pyroxmangite.

Alteration

braunite to hausmannite, SiO2 and O2
3Mn2+Mn3+6O8(SiO4) ⇌ 7Mn2+Mn3+2O4 +3SiO2 + O2

braunite to hausmannite, rhodonite and O2
2Mn2+Mn3+6O8(SiO4) ⇌ 4Mn2+Mn3+2O4 + 2Mn2+SiO3 + O2
A higher temperature favours the forward reaction

braunite to tephroite, hausmannite and O2
3Mn2+Mn3+6O8(SiO4) ⇌ 3Mn2+2(SiO4) + 5Mn2+Mn3+2O4 + 2O2

braunite and CO2 to rhodochrosite, rhodonite and O2
2Mn2+Mn3+6O8(SiO4) + 12CO2 ⇌ 12MnCO3 + 2Mn2+SiO3 + 3O2
A higher temperature favours the reverse reaction

braunite and quartz to rhodonite and O2
2Mn2+Mn3+6O8(SiO4) + 12SiO2 ⇌ 14Mn2+SiO3 + 3O2
A higher temperature favours the forward reaction

pyrolusite and quartz to braunite and O2
7Mn4+O2 + SiO2 ⇌ Mn2+Mn3+6O8(SiO4) + 2O2
A higher temperature favours the forward reaction

rhodochrosite, SiO2 and O2 to braunite and CO2
14MnCO3 + 2SiO2 + 3O2 = 2Mn2+Mn3+6O8(SiO4) ⇌ 14CO2
A higher temperature favours the forward reaction

rhodonite and braunite to tephroite and O2
10Mn2+SiO3 + 2Mn2+Mn3+6O8(SiO4) ⇌ 12Mn2+2(SiO4) + 3O2
A higher temperature favours the forward reaction

Common impurities: Fe,Ca,B,Ba,Ti,Al,Mg

Brochantite

Formula: Cu4(SO4)(OH)6 sulphate with hydroxyl
Specific gravity: 3.97
Hardness: 3½ to 4
Streak: Green to light green
Colour: Emerald green
Solubility: Moderately soluble in hydrochloric, sulphuric and nitric acid
Environments:

Hydrothermal environments

Brochantite occurs as a secondary mineral in the oxidation zone of high temperature copper ores.

Alteration

Chalcopyrite CuFeS2 (primary) readily alters to the secondary minerals bornite Cu5FeS4, covellite CuS and brochantite Cu4SO4(OH)6.

Bromargyrite

Formula: AgBr anhydrous halide
Specific gravity: 6.474
Hardness: 2½
Streak: White to yellowish white
Colour: Yellowish, greenish brown, bright green
Melting point: 434oC

Hydrothermal environments

Bromargyrite occurs in the oxidised zone of silver deposits
Common impurities: Cl, I

Bromellite

Formula: BeO Simple oxide
Specific gravity: 3.017
Hardness: 9
Streak: White
Colour: White to creamy white
Environments:

Metamorphic environments
Hydrothermal environments

Bromellite occurs in hydrothermal calcite veins and veinlets in skarn.

Localities

Norway

At Langesundsfjord, Norway, bromellite occurs in vugs in natrolite, hydrothermally altered from nepheline, in syenite pegmatite associated with natrolite, diaspore and chamosite.

Russia

Near Ekaterinburg in the Ural Mountains, Russia, bromellite has been found in an emerald mine associated with phenakite.

Sweden

At the type locality, Långban Sweden, bromellite occurs in hydrothermal calcite veins in a calcite-hematite skarn associated with swedenborgite, richterite and manganophyllite.

USA

Bromellite has been reported in skarn south of Sierra Blanca, Hudspeth County, Texas, USA

Common impurities: Al,B,Ba,Ca,Fe,Mg,Si

Brucite

Formula: Mg(OH)2 hydroxide
Specific gravity: 2.03
Hardness: 2½
Streak: White
Colour: White, grey, greenish, bluish, yellow to brown
Solubility: Readily soluble in hydrochloric, sulphuric and nitric acid
Environments:

Pegmatites
Carbonatites
Metamorphic environments

Brucite is found in limestone, marble, dolostone and slate, as an alteration product of serpentine. At Palabora, Limpopo Province, South Africa, it is found in carbonatite.
It is associated with serpentine, dolomite, magnesite and chromite.
It is a mineral of the blueschist, greenschist and amphibolite facies.

Alteration

brucite to periclase and H2O
Mg(OH)2 ⇌ MgO + H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 840oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures (for the same pressure).

brucite and antigorite to forsterite and H2O
Mg(OH)2 + Mg3Si2O5(OH)4 ⇌ 2Mg2SiO4 + 3H2O
The equilibrium temperature for this reaction at 8 kbar pressure is about 450oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures. The reaction also may occur in the albite-epidote-hornfels and blueschist facies.

forsterite and H2O to serpentine and brucite
2Mg2SiO4 + 3H2O ⇌ Mg3Si2O5(OH)4 + Mg(OH)2
The forward reaction is highly exothermic. At 5 kbar pressure the equilibrium temperature is about 420°C (greenschist facies).

Buddingtonite

Formula: (NH4)(AlSi3)O8 tectosilicate (framework silicate)

Burkeite

Formula: Na4(SO4)(CO3) compound sulphate
Specific gravity: 2.57
Hardness: 3Æ
Streak: White
Colour: White, light buff, grayish; colourless in transmitted light
Solubility: Soluble in cold water
Environment:

Sedimentary environments

Burkeite occurs in continental evaporite deposits. At Searles Lake, California, USA, it is associated with gaylussite, trona, sulphohalite, borax and northupite. At the Konya Basin, Central Anatolia, Turkey, burkeite occurs with halite and trona.

Bustamite

Formula: CaMn2+Si2O6 inosilicate (chain silicate) wollastonite group
Specific gravity: 3.32 to 3.43
Hardness: 5½ to 6½
Streak: White
Colour: Pale to medium pink; brownish red; colourless to yellowish pink in transmitted light. Pink colour fades on exposure to sunlight
Solubility: Partly soluble in hydrochloric acid
Environments:

Metamorphic environments

Bustamite occurs in manganese ores formed by metamorphism of manganese-bearing sediments. The type locality is a carbonate-silicate hosted zinc deposit. Common associates include calcite, diopside, glaucochroite, grossular, johannsenite, rhodonite and wollastonite.

Alteration

bustamite, tephroite and calcite to glaucochroite and CO2
CaMn2+Si2O6 + Mn2+2(SiO4) + 2CaCO3 ⇌ 3CaMn2+(SiO4) + 2CO2

Calcite

Formula: CaCO3 carbonate
Specific gravity: 2.7102(2)
Hardness: 3
Streak: White
Colour: Colourless, white, yellow, red, orange, blue, green, pink, purple
Solubility: Readily soluble in hydrochloric, sulphuric and nitric acid
Environments:

Pegmatites
Carbonatites (essential)
Sedimentary environments (typical)
Metamorphic environments
Hydrothermal environments
Basaltic cavities

Calcite is a common and widespread mineral. It occurs in limestone, marble and chalk, in all of which it is essentially the only mineral present. It is an important constituent of calcareous marl and calcareous sandstone. Water carrying calcium carbonate in solution and evaporating in limestone caves often deposits calcite as stalagtites, stalagmites and incrustations. Both hot and cold calcium-bearing spring water may form cellular deposits of calcite known as travertine or tufa around their mouths. Calcite occurs as a primary mineral in some igneous rocks such as nepheline syenite, carbonatites and pegmatites. It is a late crystallisation product in cavities in lavas, and it is also a common mineral in the oxidation zone of hypothermal (high temperature), mesothermal (moderate temperature) and epithermal (low temperature) hydrothermal veins associated with sulphide ores.
Carbonates such as calcite are essential constituents of kimberlite.
Calcite is an essential constituent of limestone, marl and skarn.
It is a common but not essential constituent of sandstone.
It also may be found in dolostone.

Calcite may occur in all metamorphic facies with the exception of the very high-grade eclogite facies.

Alteration

Calcite and aragonite are precipitated according to the following reactions:
Carbon dioxide in the atmosphere is dissolved in rainwater forming weak carbonic acid:
H2O + CO2 → H2CO3
Carbonic acid dissolves limestone forming calcium bicarbonate
H2CO3 + CaCO3 → Ca(HCO3)2
This solution percolates into caves where calcium carbonate may be precipitated as calcite with the release of liquid water and gaseous carbon dioxide:
Ca(HCO3)2 ⇆ CaCO3 (solid) + H2O (liquid) + CO2 (gas)
The net effect of these changes could be written as the reversible reaction
CaCO3 (solid) + H2CO3 (in solution) ⇌ Ca2+ + 2(HCO3)-
The forward reaction, solution of calcium carbonate, occurs in acid environments, and the reverse reaction, precipitation of calcium carbonate, occurs in strongly basic (alkaline) environments.

Camp Verde, Arizona, is known for pseudomorphs of calcite after glauberite.

aegirine, epidote and CO2 to albite, hematite, quartz, calcite and H2O
4NaFe3+Si2O6 + 2Ca2(Al2Fe3+[Si2O7](SiO4)O(OH) + 4CO2 → 4Na(AlSi3O8) + 3Fe2O3 + 2SiO2 + 4CaCO3 + H2O

diopside and calcite
Ca2MgSi2O7 + CO2 ⇌ CaMgSi2O6 + CaCO3
The maximum stability limit of åkermanite in the presence of excess CO2 is about 6 kbar. Below that pressure, at relatively lower temperatures, åkermanite reacts with CO2 to form diopside and calcite according to the reaction:

albite, chlorite and calcite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz, CO2 and H2O
8Na(AlSi3O8) + (Mg4.0Fe2.0)(AlSi3O10)(OH)8 + CaCO3 → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 2SiO2 + CO2 + 2H2O
In low to intermediate metamorphism jadeite-glaucophane assemblages may arise from reactions such as the one above.

calcium amphibole, calcite and quartz to diopside-hedenbergite, anorthite, CO2 and H2O
Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + 3CaCO3 + 4SiO2 = 3Ca(Fe,Mg)Si2O6 + 2Ca(Al2Si2O8) + 3CO2 + H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

amphibole, chlorite, paragonite, ilmenite, quartz and calcite to garnet, omphacite, rutile, H2O and CO2
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + Mg5Al(AlSi3O10)(OH)8 + 3NaAl2(Si3Al)O10(OH)2 + 4Fe2+Ti4+O3 + 9SiO2 + 4CaCO3 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 8H2O + 4CO2 In low-grade rocks relatively rich in calcite the garnet-omphacite association may be due to reactions such as the above.

anorthite to calcite and kaolinite in the early Earth's atmosphere
CO2 + H2O + anorthite → calcite + kaolinite
CO2 + 2H2O + CaAl2Si2O8 → CaCO3 + Al2Si2O5(OH)4

anorthite, H2O and CO2kaolinite and calcite
2CaAl2 Si2O8 + 4H2O + 2CO2 ⇌ Al4Si4O10(OH)8 + 2CaCO3
Calcite is found as a low-temperature, late-stage alteraation product according to the above reaction.

anorthite and calcite to meionite (scapolite series)
3Ca(Al2Si2O8) + CaCO3 ⇌ Ca4Al6O24(CO3)
This reaction occurs in the presence of a high CO2 pressure in an environment deficient in (Al+Na+K).

antigorite and calcite to forsterite, diopside, CO2 and H2O
3Mg3Si2O5(OH)4 + CaCO3 → 4Mg2SiO4 + CaMgSi2O6 + CO2 +6 H2O
This reaction has been found to occur in antigorite schist at about 3 kbar pressure and 400 to 500oC (greenschist facies).

aragonite or calcite and Mg2+ (from Mg-rich fluid) to dolomite and Ca2+
2CaCO3 + Mg2+ ⇌ CaMg(CO3)2 + Ca2+

augite and CO2 to hypersthene, calcite and quartz
Ca(Mg,Fe)Si2O6 + CO2 → (Mg,Fe)SiO3 + CaCO3 + SiO2

bustamite, tephroite and calcite to glaucochroite and CO2
CaMn2+Si2O6 + Mn2+2(SiO4) + 2CaCO3 ⇌ 3CaMn2+(SiO4) + 2CO2

calcite, Ba2+, H2S and O2 to baryte, Ca2+, CO2 and H2O
CaCO3 + Ba2+ + H2S + 2O2 = BaSO4 + Ca2+ + CO2 and H2O
Baryte may be precipitated by the action of ore fluid and groundwater on calcite.

calcite, Fe2+ and Mg2+ to ankerite and Ca2+
4CaCO3 + Fe2+ + Mg2+ = 2Ca(Mg0.5Fe0.5)(CO3)2+ 2Ca2+
Ankerite is believed to be formed from calcite hydrothermally according to the above reaction.

calcite, hematite and quartz to andradite and CO2
3CaCO3 + Fe2O3 + 3SiO2 → Ca3Fe3+2Si3O12 + 3CO2

calcium amphibole, calcite and quartz to diopside-hedenbergite, anorthite, CO2 and H2O
Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + 3CaCO3 + 4SiO2 = 3Ca(Fe,Mg)Si2O6 + 2Ca(Al2Si2O8) + 3CO2 + H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

diopside, CO2 and H2O to tremolite, calcite and quartz
5CaMgSi2O6 + 3CO2 + H2O = Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 2SiO2
Diopside is produced by the metamorphism of siliceous dolostone, and if water is introduced at a later stage tremolite may be produced from the above reaction, or by the reaction of diopside with dolomite.

dolomite and chert to talc and calcite
3CaMg(CO3)2 + 4SiO2 + H2O → Mg3Si4O10(OH)2 + 3CaCO3 + 3CO2
Metamorphism of siliceous carbonate rocks causes the formation of hydrous phases such as talc and tremolite. This is a very low-grade metamorphic reaction occurring at temperature between about 150oC and 250oC.

diopside and dolomite to forsterite, calcite and CO2
CaMgSi2O6 + 3CaMg(CO3)2 → 2Mg2SiO4 + 4CaCO3 + 2CO2
This is a high-grade metamorphic change occurring at temperature in excess of 600oC.

diopside, dolomite, CO2 and H2O to actinolite and calcite
4CaMgSi2O6 + CaMg(CO3)2 + CO2 + H2O = Ca2Mg5Si8O22(OH)2 + 3CaCO3
Diopside is produced by the metamorphism of siliceous dolostone, and if water is introduced at a later stage tremolite may be produced from the above reaction, or by the reaction of diopside with CO2 and H2O.

diopside, dolomite and H2O ⇌ hydroxylclinohumite, calcite and CO2
2CaMgSi2O6 + 7CaMg(CO3)2 + H2O ⇌ 4Mg2SiO4.Mg(OH)2 + 9CaCO3 + 5CO2
In the nodular dolomites, clinohumite associated with calcite occurs in a narrow zone in the central parts of the nodules due to the above reaction

diopside, forsterite and calcite to monticellite and CO2
CaMgSi2O6 + Mg2SiO4 + 2CaCO3 → 3CaMgSiO4 + 2CO2
This reaction requires a high temperature.

diopside-hedenbergite and CO2 to enstatite- ferrosilite, calcite and quartz
Ca(Mg,Fe)Si2O6 + CO2 → (Mg,Fe2+)SiO3 + CaCO3 + SiO2

dolomite, K-feldspar and H2O to phlogopite, calcite and CO2
3CaMg(CO3)2 + KAlSi3O8 + H2O = KMg3AlSi3O10(OH)2 + 3CaCO3 + 3CO2
In the presence of Al and K the metamorphism of dolomite leads to the formation of phlogopite according to the above equation.

dolomite and quartz to forsterite, calcite and CO2
2CaMg(CO3)2 + SiO2 → Mg2SiO4 + 2CaCO3 + 2CO2 In siliceous dolostone dolomite and quartz may react to form either diopside or forsterite, with diopside forming at a lower temperature than forsterite.

dolomite, quartz and H2O to tremolite, calcite and CO2
5CaMg(CO3)2 + 8SiO2 + H2O → Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 7CO2
This is a metamorphic reaction in dolomitic limestone.

dolomite and tremolite to forsterite, calcite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 11CaMg(CO3)2 → 8Mg2SiO4 + 13CaCO3 + 9CO2 + H2O
Dolomite can be metamorphosed to talc and calcite, then at higher temperatures the talc and calcite react to form tremolite. In turn tremolite reacts with dolomite to form forsterite, according to the above equation.

enstatite and calcite to forsterite, diopside and CO2
3Mg2Si2O6 + 2CaCO3 ⇌ 2Mg2SiO4 + 2CaMgSi2O6 + 2CO2
enstatite is uncommon in the more calcareous hornfels due to reactions such as the above.

enstatite, calcite and quartz to diopside and CO2
3Mg2Si2O6 + 2CaCO3 + 2SiO2 ⇌ + 2CaMgSi2O6 + 2CO2 enstatite is uncommon in the more calcareous hornfels due to reactions such as the above.

ferro-actinolite, calcite and quartz to hedenbergite, CO2 and H2O
Ca2Fe2+5Si8O22(OH)2 + 3CaCO3 + 2SiO2 ⇌ 5CaFe2+Si2O6 + 3CO2 + H2O In some calc-silicate rocks hedenbergite is the product of metamorphism of iron-rich sediments, according to the above reaction, probably due to the instability of ferro-actinolite with rising temperature.

forsterite, calcite and quartz to diopside and CO2
Mg2SiO4 + 2CaCO3 + 3SiO2 → 2CaMgSi2O6 + 2CO2
In high temperature environments with excess SiO2 diopside may form accoring to the above reaction.

forsterite, calcite and quartz to monticellite and CO2
Mg2SiO4 + 2CaCO3 + SiO2 → 2CaMg(SiO4) + 2CO2

forsterite, diopside and calcite to monticellite and CO2
Mg2SiO4 + CaMgSi2O6 + 2 CaCO3 ⇌ 3CaMg(SiO4) + 2 CO2
This reaction occurs during contact metamorphism of magnesian limestone.

forsterite and dolomite to calcite and hydroxylclinohumite
4Mg2SiO4 + CaMg(CO3)2 + H2O → Mg9(SiO4)4(OH)2 + CaCO3 + CO2
This is probably the reaction responsible for a forsterite- clinohumite assemblage in silica-rich dolomite in the aureole of the Alta granodiorite in Utah, USA.

forsterite, dolomite and H2O to calcite, hydroxylclinohumite and CO2
4Mg2SiO4 + CaMg(CO3)2 + H2O → Mg9(SiO4)4(OH)2 +CaCO3 + CO2
A forsterite-clinohumite assemblage in the silica-rich dolomite in the aureole of the Alta granodiorite in Utah, USA, is probably due to the above reaction.

grossular, diopside, monticellite, calcite and H2O to vesuvianite, quartz and CO2
10Ca3Al2(SiO4)3 + 3CaMgSi2O6 + 3CaMg(SiO4) + 2CaCO3 + 8H2O ⇌ 2Ca19Al10Mg3(SiO4)10 (Si2O2)4O2(OH)8 + 3SiO2 + 2CO2 A common association in calc-silicate metamorphism can be represented by the above equation. Vesuvianite stability will tend to increase with increasing water and decrease as the activity of CO2 rises.

hematite, wüstite, quartz and calcite to andradite, hedenbergite magnetite and CO2
2Fe2O3 + 2FeO + 5SiO2 + 4CaCO3 → Ca3Fe3+2(SiO4)3 + CaFe2+Si2O6 +Fe2+Fe3+2O4 +4CO2

hornblende, calcite and quartz to Fe-rich diopside, anorthite, CO2 and H2O
Ca2(Mg,Fe2+)3(Al4Si6)O22(OH)2 + 3CaCO3 + 4SiO2 = 3Ca(Mg,Fe2+)Si2O6 + 2Ca(Al2Si2O8) + 3CO2 + H2O
Fe-rich diopside occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies. The above reaction is typical.

kaolinite, dolomite, quartz and H2O to chlorite, calcite and CO2
Al2Si2O5(OH)4 + 5CaMg(CO3)2 + SiO2 + 2H2O ⇌ Mg5Al(AlSi3O10)(OH)8 + 5CaCO3 + 5CO2
Chlorite often forms in this way from reactions between clay minerals such as kaolinite and carbonates such as dolomite.

laumontite and calcite to prehnite, quartz, H2O and CO2
CaAl2Si4O12.4H2O + CaCO3 → Ca2Al(Si3Al)O10(OH)2 + SiO2 + 3H2O + CO2
Prehnite and pumpellyite form from the Ca zeolites in the presence of calcite, as in the above equation.

meionite (scapolite series) and augite to garnet, calcite and quartz
Ca4Al6O24(CO3) + 3Ca(Mg,Fe2+)Si2O6 ⇌ 3Ca2(Mg,Fe2+)Al2(SiO4)3 + CaCO3 + 3SiO2

meionite (scapolite series), calcite and quartz to grossular and CO2
Ca4Al6O24(CO3) + 5CaCO3 + 3SiO2 ⇌ 3Ca3Al2(SiO4)3 + 6CO2

monticellite and CO2 to åkermanite, forsterite and calcite
3CaMgSiO4 + CO2 ⇌ Ca2MgSi27 + Mg2O7 + CaCO3
At 4.3 kbar pressure the equilibrium temperature is about 890oC (granulite facies).

monticellite and spurrite to merwinite and calcite
2CaMg(SiO4) + Ca5(SiO4)2(CO3) ⇌ 2Ca3Mg(SiO4)2 + CaCO3

phlogopite, calcite and quartz to diopside, microcline, H2O and CO2
KMg3(AlSi3O10)(OH)2 + 3CaCO3 + 6SiO2 = 3CaMgSi2O6 + K(AlSi3O8) + H2O + 3CO2
In reaction zones between interbedded carbonate and pelitic beds of the calc-mica schists, phlogopite may alter according to the above reaction.

quartz and calcite to wollastonite and CO2
3SiO2 + 3CaCO3 ⇌ Ca3Si3O9 + 3CO2 (gaseous)
This is a contact metamorphic change occurring at temperatures from about 600°C such as in the immediate border zone of an igneous intrusion into limestone. High pressure inhibits the forward reaction by suppressing the formation of gaseous CO2. At 10 kbar pressure the equilibrium temperature is about 1,070oC (granulite facies).

talc and calcite to dolomite and quartz
talc + calcite + CO2dolomite + quartz + H2O
Mg3Si4O10(OH)2 + 3CaCO3 + 3CO2 ⇌ 3CaMg(CO3)2 + 4SiO2 + H2O

talc and calcite to tremolite dolomite, CO2 and H2O
2Mg3Si4O10(OH)2 + 3CaCO3 +4SiO2 → Ca2Mg5Si8O22(OH)2 + CaMg(CO3)2 + CO2 +H2O
This is a low-grade metamorphic change, occurring at temperature between about 250oC and 450oC.

talc, calcite and quartz to tremolite, CO2 and H2O
5Mg3Si4O10(OH)2 + 6CaCO3 +4SiO2 → 3Ca2Mg5Si8O22(OH)2 + 6CO2 +2H2O
Metamorphism of siliceous carbonate rock causes the formation of hydrous phases such as talc and tremolite.

tremolite and calcite to diopside, dolomite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 3CaCO3 ⇌ 4CaMgSi2O6 + CaMg(CO3)2 + CO2 + H2O
The forward reaction is a diopside-forming metamorphic reaction.

tremolite, calcite and quartz to diopside, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 2SiO2 → 5CaMgSi2O6 + 3CO2 + H2O
This is a medium-grade metamorphic change occurring at temperature between about 450oC and 600oC.

tremolite and dolomite to forsterite, calcite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 11CaMg(CO3)2 → 8Mg2SiO4 + 13CaCO3 + 9CO2 + H2O

tremolite, dolomite and H2O ⇆ hydroxylclinohumite, calcite and CO2
Ca2Mg5Si8O22(OH)2 + 13CaMg(CO3)2 + H2O ⇆ 2(4Mg2SiO4.Mg(OH)2) + 15CaCO3 + 11CO2

Common impurities: Mn,Fe,Zn,Co,Ba,Sr,Pb,Mg,Cu,Al,Ni,V,Cr,Mo

Caledonite

Formula: Cu2Pb5(SO4)3(CO3)(OH)6 compound sulphate
Specific gravity: 5.75 to 5.77
Hardness: 2½ to 3
Streak: Greenish-blue to bluish-white, paler than the sample
Colour: Dark blue to bluish-green; light bluish green in transmitted light
Solubility: Soluble in nitric acid with effervescence

Hydrothermal environments

Caledonite is an uncommon secondary mineral in the oxidised portions of Pb–Cu deposits. Alteration to cerussite has been observed.

Localities

Australia

At Pilbara, Western Australia, caledonite occurs associated with linarite, cerussite, brochantite and malachite. It sometimes forms a massive coating on cerussite.

United Kingdom

Caledonite occurs at many localities in Caldbeck, Cumbria, England.
- At Balliway Rigg it occurs in a quartz-galena matrix associated with leadhillite and its polymorph susannite, and the rare mineral mattheddleite Pb5(SiO4)1.5(SO4)1.5Cl; it also occurs in cavities in vein quartz with linarite, leadhillite and susannite.
- At Brae Fell Mine it occurs associated with linarite, or with leadhillite and cerussite.
- At Driggith Mine it occurs with leadhillite and linarite, or with linarite in oxidation rims surrounding galena.
- At Red Gill Mine it occurs in cavities in quartz associated with leadhillite, linarite, cerussite, anglesite and mattheddleite, Pb5(SiO4)1.5(SO4)1.5Cl which is very rare worldwide, but not uncommon here.

USA

In the Otto Mountains, Baker, California, caledonite is sometimes associated with linarite.

Cancrinite

Formula: Na,Ca,☐)8(Al6Si6)O24 (CO3,SO4)2.2H2O
Tectosilicate (framework silicate), feldspathoid
Specific gravity:
Hardness: 5 to 6
Streak: White
Colour: Grey-green, white, yellow, blue, orange, reddish
Solubility: It is unusual among the silicate minerals in that it is moderately soluble in hydrochloric acid due to the carbonate ions in its structure.
Environments:

Plutonic igneous environments
Pegmatites
Hydrothermal environments

Cancrinite is a primary mineral in some alkaline igneous rocks, including pegmatites in nepheline syenites. It is also an alteration product of nepheline in igneous rocks

Common impurities: Ti,Fe,Mg,K,Cl,S

Carminite

Formula: PbFe3+2(AsO4)2(OH)2

Carpholite

Formula: Mn2+Al2Si2O6(OH)4 inosilicate (chain silicate)
Specific gravity: 3.0
Hardness: 5 -5½
Streak: White
Colour: Straw-yellow
Environments:

Metamorphic environments
Hydrothermal environments

Carpholite occurs in hydrothermal veins in tin deposits. It is a mineral of the eclogite facies.

Cassiterite

Formula: SnO2 simple oxide, rutile group
Specific gravity: 6.98 to 7.01
Hardness: 6 to 7
Streak: Brownish white, white, greyish
Colour: Black, yellow, brown, red or white.
Solubility: Slightly soluble in hydrochloric and nitric acid; insoluble in sulphuric acid
Environments:

Plutonic igneous environments
Pegmatites
Placer deposits
Hydrothermal environments

Cassiterite is widely distributed. It occurs as a primary mineral in igneous rocks and pegmatites but it is more commonly found as an unaltered primary mineral in hypothermal (high temperature) hydrothermal quartz veins of tin deposits in or near granitic rocks. Because of its durability it is also found frequently in placer deposits.
In high temperature quartz veins associated with granitic intrusions cassiterite is often associated with ferberite, molybdenite and arsenopyrite.
At Llallague, Bolivia, cassiterite in hydrothermal veins crystallises at about 300oC.

Common impurities: Fe,Ta,Nb,Zn,W,Mn,Sc,Ge,In,Ga

Cavansite

Formula: Ca(V4+O)(Si4O10).4H2O phyllosilicate (sheet silicate)
Specific gravity: 2.21 to 2.31
Hardness: 3 to 4
Streak: Bluish white
Colour: Blue to greenish blue
Solubility: Slightly soluble in acids
Environments:

Volcanic igneous environments
Sedimentary environments

Cavansite occurs in zeolites in basalt, and also in Tuff. At Lake Owyhee State Park cavansite occurs in fractures in tuff, associated with zeolites and calcite. Near Pua, India, it occurs in silica-rich breccia.

Celadonite

Formula: KMgFe3+Si4O10(OH)2 phyllosilicate (sheet silicate), mica group
Specific gravity: 2.95 to 3.05
Hardness: 2
Streak: Greenish white
Colour: Blue-green, olive green, apple green
Environments:

Metamorphic environments
Basaltic cavities

Celadonite occurs as vesicle lining and coatings in altered volcanic rocks of intermediate to basic compositions, under low grade metamorphism.
Common impurities: Mn,Ca,Na

Celestine

Formula: Sr(SO4) sulphate
Specific gravity: 3.9 to 4.0
Hardness: 3 to 3½
Streak: White
Colour: Colourless, white, blue, reddish, greenish, brownish
Solubility: Slightly soluble in hydrochloric, sulphuric and nitric acid
Environments:

Volcanic igneous environments
Sedimentary environments
Hydrothermal environments (occasionally)
Basaltic cavities

Celestine is usually found disseminated through limestone or sandstone, or lining cavities in such rocks. It is also found occasionally in hydrothermal replacement environments and in vesicles in vocanic rocks.
It is often associated with calcite, dolomite, gypsum, halite, sulphur and fluorite. Celestine occurs either as a primary precipitate from aqueous solutions or, more usually, by the interaction of gypsum or anhydrite with Sr-rich waters. Beds of celestine are therefore commonly found immediately above or below gypsum or anhydrite deposits.

Celsian

Formula: Ba(Al2Si2O8)
Tectosilicate (framework silicate), feldspar group, dimorph of paracelsian
Specific gravity: 3.10 to 3.45
Hardness: 6 to 6½
Streak: White
Colour: Colourless, white, yellow

Metamorphic environments

Celsian occurs in amphibolite grade metamorphic rocks rich in manganese and barium.
It is associated with manganese-rich aegirine and biotite, paracelsian, jacobsite, hausmannite, rhodochrosite, rhodonite, rutile, hyalophane, baryte, cymrite, taramellite, quartz, zoisite, spessartine, dolomite and muscovite

At Broken Hill, New South Wales, Australia, celsian has been described from lenses and streaks in acid gneiss associated with plagioclase.
In the manganese ores of Otjosondu, Namibia, celsian is associated with a vredenburgite-garnet rock.
At the Benallt manganese mine at Rhiw, Wales, UK, celsian and paracelsian occur in a band in shale and sandstone associated with beds of manganese ore.

Common impurities: Fe,Mg,Ca,Na,K,F

Cerussite

Formula: Pb(CO3) carbonate
Specific gravity: 6.4 - 6.6
Hardness: 3 to 3½
Streak: White
Colour: Colourless, white, grey, yellow, brown, blackish (from inclusions of galena)
Solubility: Slightly soluble in hydrochloric acid and sulphuric acid; moderately soluble in nitric acid
Environments:

Carbonatites
Hydrothermal environments

Cerussite is generally a secondary mineral that occurs in the oxidation zone of high temperature lead-zinc deposits. It also occurs as alteration pseudomorphs after anglesite, phosgenite, leadhillite, caledonite, hydrocerussite, bournonite, linarite, pyromorphite and vanadinite. and also as substitution pseudomorphs after calcite and sphalerite.

Lead will generally precipitate as primary galena from ore fluids rich in sulphur and lead. Removal of sulphur by precipitation of sulphides, however, may lead ultimately to an ore fluid from which galena cannot be precipitated, even with a high concentration of lead in solution. In these circumstances, cerussite, as well as pyromorphite and anglesite, could be precipitated as a primary mineral.

Alteration

In the oxidation zone of epithermal veins primary galena PbS alters to secondary cerussite PbCO3 or anglesite depending on the acidity. Cerussite forms in more basic (alkaline) environments than anglesite.

Formation of cerussite
Galena may dissolve in carbonic acid from percolating rainwater to form lead ions, Pb2+.
PbS + 2H2CO3 → Pb2+ + H2S + 2HCO3>-
These lead ions may then combine with carbonate ions CO32- to form cerussite, which is virtually insoluble in water and weak acids.
Pb2+ + CO3>2- → PbCO3

cerussite and aqueous H2AsO4-, Cl- and H+ to mimetite and aqueous H2CO3
5PbCO3 + 3H2AsO4- + Cl- + 7H+ ⇌ Pb5(AsO4)3Cl + 5H2CO3
or
5PbCO3 + 3HAsO42- + Cl- + 4H+ ⇌ Pb5(AsO4)3Cl + 5H2CO3
cerussite and mimetite can co-exist only under basic conditions at rather high PCO2.

Chabazite

The chabazite series comprises five mineral species:
Chabazite-Ca: Ca2[Al4Si8O24]. 13H2O
Chabazite-K: (K2NaCa0.5)[Al4Si8 O24].11H2O
Chabazite-Mg: (Mg0.7K0.5 Na0.1)[Al3Si9O24].10H2O
Chabazite-Na: (Na3K)[Al4Si8O24].11H2 O
Chabazite-Sr: (Sr,Ca)2[Al4Si8O24]. 11H2O
These are all tectosilicates (framework silicates), zeolite group
Specific gravity: 2.08
Hardness: 4½
Streak: White
Colour: Colourless, white, yellow, orange, brown
Solubility: Moderately soluble in hydrochloric acid
Environments:

Pegmatites
Basaltic cavities

Chabazite is found in cavities in basalt associated with stilbite, mesolite, mordenite, heulandite and apophyllite; it is also found in pegmatites.
It is a low temperature mineral. Geothermal wells have been drilled through a thick series of basalt flows in western Iceland, where it was found that chabazite crystallised at temperatures from 55oC to 75oC at depths between 50m and 400m.

At Willy Wally Gully, New South Wales, Australia, it typically occurs alone in vesicles in basalt, but occasionally it is associated with apatite, lévyne-Ca/offretite, phillipsite, aragonite and/or calcite. It is only rarely associated with more than one other zeolite in the same vesicle.

At Rollinsons Quarry, Victoria, Australia, late forming chabazite-Ca was found in some cavities in basalt associated with augite and anorthoclase.

In Moravia, Czech Republic, chabazite occurs in cavities with axinite, epidote, natrolite, heulandite and stilbite.

At Palabora, South Africa, chabazite-Ca is found associated with analcime, fluorapophyllite and heulandite.

In Honolulu, Hawaii, USA, chabazite occurs in basaltic cavities with phillipsite, magnetite and calcite.

At a road cut prehnite occurrence on the Russell-Hermon Road, St Lawrence County, New York, chabazite-Ca occurs rarely, associated with quartz and calcite.

Chalcedony

Chalcedony is a variety of quartz.
Formula: SiO2 tectosilicate (framework silicate)
Specific gravity: 2.6
Hardness: 6½; to 7
Streak: White
Colour: Colourless, white, gray, blue, any colour due to embedded minerals; multicoloured specimens not uncommon.
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Volcanic igneous environments
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Chalcedony is deposited from aqueous solutions, and is frequently found lining or filling cavities in volcanic rocks, as crusts in epithermal (low temperature) to mesothermal (medium temperature) hydrothermal veins, as a constituent of silica-rich marine sedimentary rocks, and as nodular concretions and layers in limestone and marl.

Chalcanthite

Formula: Cu(SO4).5H2O sulphate
Specific gravity: 2.2 to 2.3
Hardness: 2Æ
Streak: Blue
Colour: Blue
Solubility: Readily soluble in water, hydrochloric, sulphuric and nitric acid
Environments:

Hydrothermal environments

Chalcanthite is a secondary mineral that is found in the oxidation zone of copper deposits, usually in arid regions where it is not dissolved by ground water. It is formed by the oxidation of chalcopyrite and other copper sulphates. It is often found as a post-mining deposit on mine walls, where it crystallises from mine waters.

Common impurities: Fe,Mg,Co

Chalcocite

Formula: Cu2S sulphide
Specific gravity: 5.7 to 5.8
Hardness: 2½ to 3
Streak: Blackish to dark grey
Colour: Dark lead grey to blackish
Solubility: Moderately soluble in nitric acid
Environments:

Metamorphic environments
Hydrothermal environments

Chalcocite may occur as a primary mineral in veins with bornite, chalcopyrite, enargite and pyrite, but its principal occurrence is as a secondary, supergene mineral in enriched zones of mesothermal (moderate temperature) and hypothermal (high temperature) sulphide deposits. Under surface conditions the primary copper sulphides are oxidised; the soluble sulphates so formed move downwards, reacting with the primary minerals to form chalcocite, enriching the ore in copper. The water table is the lower limit of the zone of oxidation and a chalcocite selfet may form here.

Alteration

Oxidation of pyrite forms ferrous (divalent) sulphate and sulphuric acid:
pyrite + oxygen + water → ferric sulphate + sulphuric acid
FeS2 + 7O + H2O → FeSO4 + H2SO4
The ferrous (divalent) sulphate readily oxidizes to ferric (trivalent) sulphate and ferric hydroxide:
ferrous sulphate + oxygen + water → ferric sulphate + ferric hydroxide
6FeSO4 + 3O + 3H2O → 2Fe2(SO4)3 + 2Fe(OH)3
Ferric sulfate is a strong oxidizing agent; covellite is formed from chalcocite by the reaction below.
chalcocite and ferrous sulphate to copper sulphate, ferrous sulphate and covellite
Cu2S + Fe2(SO4)3 → CuSO4 + 2FeSO4 + CuS

chalcopyrite and chalcocite to bornite
CuFe3+S2 + 2Cu2S = Cu5FeS4

Common impurities: Fe

Chalcophyllite

Formula: Cu18Al2(AsO4)4(SO4)3(OH)24.36H2O
Compound arsenate, water content varies at room temperature based on the relative humidity.
Specific gravity: 2.67
Hardness: 2
Streak: Pale green
Colour: Blue-green to emerald green
Solubility: Soluble in acids and in ammonia.
Environments:

Hydrothermal environments
Basaltic cavities

Chalcophyllite is an uncommon secondary supergene copper mineral occurring in the oxidised zones of some arsenic-bearing hydrothermal polymetallic deposits.
Associates include azurite, malachite, brochantite, chrysocolla, spangolite, connellite, cuprite, cyanotrichite, strashimirite, parnauite, lavendulan, cornubite, langite, clinoclase, pharmacosiderite, and mansfieldite.
Alteration: Chalcophyllite alters to chrysocolla.

Localities

Austria

At the Silberberg mining district, Austria, chalcophyllite occurs with tyrolite, azurite, and brochantite.

Chile

At the El Teniente mine, Cachapoal Province, Chile, chalcophyllite has been found, often on partially corroded tennantite, associated with cornubite, connellite, goethite, gypsum, olivenite and tenorite.

France

At the St Jean mine, Bourgogne-Franche-Comté, France, chalcophyllite can be found on iron oxide–quartz matrix, occasionally associated with chrysocolla and mixite.

In the gold mines of the Salsigne district, Occitanie, France, chalcophyllite occurs in the oxide zone with other arsenates such as scorodite.

Italy

At the Gambatesa mine, Liguria, Italy, chalcophyllite has been reported from secondary copper assemblages on altered tennantite.

At the Scrava mine, Val Graveglia manganese district, Liguria, Italy, chalcophyllite is found associated with clinoclase, cornubite, cornwallite, lavendulan, olivenite, and tyrolite.

Morocco

At the Aghbar mine, Bou Azzer district, Ouarzazate Province, Morocco, chalcophyllite has been reported on pink dolomite.

United Kingdom - England

At Wheal Gorland, St Day, Cornwall, England, chalcophyllite occurs in the oxide zone lining cavities with chrysocolla, cuprite, and malachite. A specimen has also been found where chalcophyllite partially replaces liroconite.

At Wheal Unity, St Day, Cornwall, England, chalcophyllite has been collected, some partially replaced by chrysocolla.

At Pemberthy Croft mine, St Hilary, Cornwall, England, chalcophyllite occurs associated with arsenopyrite, chalcocite, chrysocolla, pharmacosiderite and scorodite.

At Wheal Cock, St Just, Cornwall, England, chalcophyllite occurs on samples of quartz and iron oxide veins in the mine dump, associated with cornwallite and other arsenates.

At New Cliffe quarry, Stanton under Bardon, Leicestershire, England, chalcophyllite occurs with azurite.

United Kingdom - Wales

At a test mine near Dolgellau, Gwynedd, Wales, chalcophyllite occurs associated with devilline, malachite, and tyrolite.

At Dyfngwm mine, Machynlleth, Powys, Wales, chalcophyllite occurs associated with brochantite, langite and linarite.

United States

Chalcophyllite occurs at Bisbee, Cochise County, Arizona, USA associated with cuprite, copper, connellite, and iron oxides, and it is also found rarely in association with cuprite nodules.

Chalcophyllite occurs as crystals in basaltic cavities in the Turtle Mountain area of Graham County, Arizona, USA.

At the Majuba mine, Antelope district, Pershing County, Nevada, USA, chalcophyllite occurs in secondary copper-rich cavities in silicified rhyolite associated with azurite, brochantite, cornwallite, connellite, cuprite and spangolite.

At the Peavine district, Washoe County, Nevada, USA, chalcophyllite occurs with tyrolite on a quartz and phyllite host rock.

At the Pyramid district, Washoe County, Nevada, USA, chalcophyllite occurs with pharmacosiderite, tyrolite, and other arsenates.

At the Ajax mine and the Mammoth mine, Tintic district, Juab County, Utah, USA, chalcophyllite occurs in the oxide zone of massive sulphide deposits associated with brochantite, cornwallite, strashimirite, malachite, and chrysocolla

Chalcopyrite

Formula: CuFeS2 sulphide
Specific gravity: 4.1 to 4.3
Hardness: 3½ to 4
Streak: Greenish black
Colour: Brass yellow, often with an iridescent tarnish
Solubility: Moderately soluble in nitric acid
Environments:

Plutonic igneous environments
Carbonatites
Metamorphic environments
Hydrothermal environments

Chalcopyrite is the most widely occurring copper mineral. It is a primary mineral.
In contact metamorphic environments it may be associated with molybdenite.
In hypothermal (high temperature) and mesothermal (moderate temperature) veins and replacement deposits it occurs associated with galena, sphalerite and dolomite. It may contain gold or silver. Chalcopyrite is often present in large bodies of pyrite. Primary chalcopyrite readily alters to the secondary minerals bornite, covellite and brochantite, and also malachite, azurite, langite and numerous other secondary copper minerals.
It occurs in carbonatite at Palabora, South Africa.

Alteration

Chalcopyrite may alter to covellite.

Oxidation of pyrite forms ferrous (divalent) sulphate and sulphuric acid:
pyrite + oxygen + water → ferric sulphate + sulphuric acid
FeS2 + 7O + H2O → FeSO4 + H2SO4
The ferrous (divalent) sulphate readily oxidizes to ferric (trivalent) sulphate and ferric hydroxide:
ferrous sulphate + oxygen + water → ferric sulphate + ferric hydroxide
6FeSO4 + 3O + 3H2O → 2Fe2(SO4)3 + 2Fe(OH)3
Ferric sulfate is a strong oxidizing agent; it oxidises chalcopyrite according to the reaction below.

chalcopyrite and ferric sulphate to copper sulphate, ferrous sulphate and sulphur
CuFeS2 + 2Fe2(SO4)3 → CuSO4 + 5FeSO4 + 2S

chalcopyrite and chalcocite to bornite
CuFe3+S2 + 2Cu2S = Cu5FeS4

Common impurities: Ag,Au,In,Tl,Se,Te

Chlorargyrite

Formula: AgCl chloride
Specific gravity: 5.5 to 5.6
Hardness: 1½
Streak: White to grey
Colour: Colourless, white, yellowish, brownish, grey, black
Melts at 455°
Environments:

Hydrothermal environments

Chlorargyrite is a secondary mineral found in the oxidation zone of silver deposits, especially in arid regions, and in epithermal (low temperature) veins. It is found associated with native silver, cerussite and other secondary minerals.

At Broken Hill, New South Wales, Australia, chlorargyrite occurs in vuggy coronodite Pb(Mn4+6Mn3+2)O16 with goethite, sometimes associated with smithsonite. It is also found with cerussite, dolomite and malachite. At deeper levels it is a late-stage mineral in the arsenate zones, associated with carminite PbFe3+2(AsO4)2(OH)2 and members of the segnitite to beudantite series.

Chlorargyrite and bromargyrite AgBr occur sparingly at the San Rafael Mine, Nevada, USA, associated with mimetite, anglesite and bayldonite.

Common impurities: I

Chlorite

Chlorite refers to a group of minerals, the most common members being
clinochlore: Mg5Al(AlSi3O10)(OH)8 and
chamosite: (Fe2+,Mg,Al,Fe3+)6(Si,Al)4 O10(OH,O)8
phyllosilicates (sheet silicates) chlorite group
Specific gravity: 2.6 to 3.3
Hardness: 2
Streak: Green, more rarely brown
Colour: Dark green to brown
Solubility: Slightly soluble in sulphuric acid
Environments:

Metamorphic environments (typical)
Hydrothermal environments
Basaltic cavities

Chlorite is a common mineral in metamorphic rocks, such as chlorite schist; it is also formed by hydrothermal alteration of igneous rocks often associated with quartz and siderite; it is found in cavities in igneous volcanic rocks and mixed with clay minerals in argillaceous sediments. At Palabora, South Africa, it occurs in mineralised cavities in carbonatite.
Chlorite is an essential constituent of phyllite.
It also may be found in hornfels.
Commonly associated minerals are actinolite and epidote, and an assemblage of quartz, albite, sericite and garnet.
Chlorite is characteristic of the greenschist facies; it is also a mineral of the zeolite, albite-epidote-hornfels, prehnite-pumpellyite, amphibolite and blueschist facies.
At the Pyrites Mica mine, St Lawrence county, New York, USA, clinochlore forms as an alteration product on the surface of some crystals of meonite, and also as an outer rind on large plates of phlogopite.

Alteration

Chlorite forms as an alteration product of Mg-Fe silicates such as pyroxene, amphibole, biotite and garnet.

albite, chlorite and calcite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz, CO2 and H2O
8Na(AlSi3O8) + (Mg4.0Fe2.0)(AlSi3O10)(OH)8 + CaCO3 → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 2SiO2 + CO2 + 2H2O
In low to intermediate metamorphism jadeite-glaucophane assemblages may arise from reactions such as the one above.

Ca-Fe amphibole, anorthite and H2O to chlorite, epidote and quartz
CaFe5Al2Si7O22(OH)2 + 3CaAl2Si2O8 + 4H2O → Fe5Al2Si3O10(OH)8 + 2Ca2Al3Si3O12(OH) + 4SiO2

amphibole, chlorite, paragonite, ilmenite, quartz and calcite to garnet, omphacite, rutile, H2O and CO2
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + Mg5Al(AlSi3O10)(OH)8 + 3NaAl2(Si3Al)O10(OH)2 + 4Fe2+Ti4+O3 + 9SiO2 + 4CaCO3 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 8H2O + 4CO2
In low-grade rocks relatively rich in calcite the garnet-omphacite association may be due to reactions such as the above.

amphibole, clinozoisite, chlorite, albite, ilmenite and quartz to garnet, omphacite, rutile and H2O
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + 2Ca2Al3[Si2o7][SiO4]O(OH) + Mg5Al(AlSi3O10)(OH)8 + 3NaAlSi3O8 + 4Fe2+Ti4+O3 + 3SiO2 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 6H2O
In low-grade rocks relatively poor in calcite the garnet-omphacite association may be developed by the above reaction.

chlorite, muscovite and quartz to biotite, Fe-rich cordierite and H2O
(Mg,Fe2+)5Al(AlSi3O10)(OH)8 + KAl2(AlSi3O10)(OH)2 + 2SiO2 → K(Mg,Fe2+)3(AlSi3O10)(OH)2 + (Mg,Fe2+)2Al4Si5O18 + 4H2O
This reaction ocurs when the metamorphic grade increases

chlorite and quartz to enstatite- ferrosilite, Fe-rich cordierite and H2O
(Mg,Fe2+)4Al4Si2O10(OH)8 + 5SiO2 → 2(Mg,Fe2+)SiO3 + (Mg,Fe2+2)2Al4Si5O18 + 4H2O
enstatite-ferrosilite also occurs in medium grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content according to the above equation.

epidote and chlorite to hornblende and anorthite
6Ca2Al3(SiO4)3(OH) + Mg5Al2Si3O18(OH)8 → Ca2Mg5Si8O22(OH)2 + 10CaAl2Si2O8
This reaction represents changes when the metamorphic grade increases from the greenschist facies to the amphibolite facies.

kaolinite, dolomite, quartz and H2O to chlorite, calcite and CO2
Al2Si2O5(OH)4 + 5CaMg(CO3)2 + SiO2 + 2H2O ⇌ Mg5Al(AlSi3O10)(OH)8 + 5CaCO3 + 5CO2
Chlorite often forms in this way from reactions between clay minerals such as kaolinite and carbonates such as dolomite.

Common impurities: clinochlore: Cr,Ca; chamosite: Mn,Ca,Na,K

Chloritoid

Formula: Fe2+Al2O(SiO4)(OH)2 nesosilicate (insular SiO4 groups)
Specific gravity: 3.4 to 3.8
Hardness: 6½
Streak: Colourless, green, grey
Colour: Dark green to green-gray or nearly black.
Solubility: Insoluble in water; soluble in sulphuric acid with decomposition
Environments:

Metamorphic environments

Chloritoid is a relatively common constituent of low to medium-grade regionally metamorphosed clay-rich rocks, particularly those rich in aluminium and ferric iron, and poor in calcium, magnesium, potassium and sodium, and it sometimes occurs due to contact metamorphism of marble.
Chloritoid may be found in phyllite, schist and marble.
In regional metamorphic environments it generally occurs as large crystals in a finer-grained matrix in association with muscovite, chlorite, staurolite, garnet and kyanite.
In contact metamorphism of marble, it may be associated with corundum and quartz, and also it sometimes occurs with corundum in emery deposits.
In metamorphic environments chloritoid first appears at the beginning of the greenschist facies, and it is also a mineral of the blueschist and eclogite facies.

Alteration

chloritoid and quartz to staurolite, almandine and H2O
23Fe2+Al2O(SiO4)(OH)2 + 8SiO2 ⇌ 4Fe2+2Al9Si4O23(OH) + 5Fe2+3Al2(SiO4)3 + 21H2O

Chlorophoenicite

Formula: (Mn,Mg,Zn)3Zn2(AsO4)(OH,O)6
Anhydrous arsenate containing hydroxyl
Specific gravity: 3.46
Hardness: 3½
Streak: Colourless
Colour: Usually colorless to whiteor light gray-green in natural light; pink to light purplish red in strong artificial light
Solubility: Soluble in acids
Environments:

Metamorphic environments
Hydrothermal environments

Chlorophoenicite is found in massive franklinite-willemite ore at Franklin, New Jersey, USA, with calcite, leucophoenicite, tephroite, gageite, and pyrochroite, and in secondary veinlets in massive ore in a metamorphosed sedimentary Zn-Fe-Mn deposit at the type locality, Buckwheat pit, Franklin Mine, Franklin, New Jersey, USA, associated with leucophoenicite, hodgkinsonite, hetaerolite, tephroite, gageite, sclarite, pyrochroite, willemite, zincite, calcite, baryte and franklinite.

Chondrodite

Formula: Mg5(SiO4)2F2 nesosilicate (insular SiO4 groups)
Specific gravity: 3.1 to 3.2
Hardness: 6 - 6½
Streak: White
Colour: Yellow, brown, red, rarely green
Solubility: Slightly soluble in hydrochloric acid
Environments:

Carbonatites (rarely)
Metamorphic environments (typically)

Chondrodite occurs in contact or regionally metamorphosed dolomitic limestone or dolostone, associated with diopside, spinel and phlogopite.
It also may be found in serpentinite associated with magnetite, and in skarn associated with wollastonite, forsterite and monticellite.
At Palabora, Limpopo Province, South Africa, chondrodite occurs atypically in carbonatite, associated with calcite, magnetite, clinochlore and less commonly with iowaite Mg6Fe3+2(OH)16Cl2.4H2O.

Common impurities: Ti,Al,Mn

Chromite

Formula: Fe2+Cr2O4 multiple oxide, spinel group
Specific gravity: 4.5 to 4.8
Hardness: 5½
Streak: Brown
Colour: Brownish black to iron black
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Sedimentary environments
Placer deposits

Chromite is a common constituent of peridotite and other mafic rocks and of serpentine derived from them. It is one of the first minerals to separate from a cooling magma.

Alteration

Fe and Cr-rich spinel , diopside and enstatite to forsterite, anorthite and chromite
MgFeAl2Cr2O8 + CaMgSi2O6 + Mg2Si2O6 ⇌ 2Mg2SiO4 + Ca(Al2Si2O8) + Fe2+Cr2O4 This reaction occurs at fairly low temperature and pressure.

Common impurities: Mg,Mn,Zn,Al,Ti

Chrysoberyl

Formula: BeAl2O4 multiple oxide
Specific gravity: 3.75
Hardness: 8½
Streak: White
Colour: Green shades, emerald-green, greenish white, yellowish green, greenish brown, yellow, blue
Environments:

Pegmatites
Metamorphic environments
Hydrothermal environments

Chrysoberyl is normally found in pegmatites, and rarely in some fluorite-rich veins. The colour-change variety alexandrite is usually found in mica schist.

Localities

Brazil

At Carnaiba the variety alexandrite occurs in schist associated with emerald.

Switzerland

Near St Gothard chrysoberyl occurs in dolostone with corundum.

USA

At many localities in Maine chrysoberyl occurs with columbite, tourmaline, gahnite and beryl.

Common impurities: Fe,Cr,Ti

Chrysocolla

Formula: (Cu2-xAlx)H2-xSi2O5 (OH)4.nH2O phyllosilicate (sheet silicate)
Specific gravity: 2.0 to 2.2
Hardness: 2 to 4
Streak: Greenish white
Colour: Light blue, blue, greenish blue
Solubility: Slightly soluble in hydrochloric, sulphuric and nitric acid. Insoluble in water.
Environments:

Hydrothermal environments

Chrysocolla is a secondary mineral that forms in the oxidation zone of all types of hydrothermal deposits, often encrusting or replacing earlier secondary minerals. It is associated with malachite, azurite, cuprite and native copper.

Chrysotile

Formula: Mg3Si2O5(OH)4 phyllosilicate (sheet silicate), serpentine group
Specific gravity: 2.0 to 2.6
Hardness: 2½ to 4
Streak: White
Colour: Green, grey to black, white, brownish
Solubility: Insoluble in water, nitric and sulphuric acid; soluble in hydrochloric acid forming an insoluble silica gel
Environments:

Metamorphic environments

Chrysotile is a major constituent of serpentinite, that is usually formed at very low temperature from peridotite by low-grade metamorphism. It occurs with other serpentine minerals such as antigorite and lizardite.

Alteration

See results for serpentine, which is a group of minerals including antigorite, chrysotile and lizardite, all of which share the same formula, although they have slightly different structures.

Cinnabar

Formula: HgS sulphide
Specific gravity: 8.1
Hardness: 2 2½
Streak: Red
Colour: Red
Solubility: Insoluble in hydrochloric acid, sulphuric and nitric acid
Environments:

Metamorphic environments
Fumeroles and hot spring deposits
Hydrothermal environments

Cinnabar occurs in the oxidation zone of epithermal (low temperature) hydrothermal veins, at fumeroles, and also in hot springs. It may be associated with baryte, native mercury, pyrite, marcasite, opal, quartz, realgar, stibnite, and sulphides of copper. Cinnabar is the most important ore of mercury but is found in quantity at comparatively few locations.

Clinoclase

Formula: Cu3(AsO4)(OH)3
Anhydrous arsenate containing hydroxyl
Specific gravity: 4.38
Hardness: 2½ to 3
Streak: Bluish green
Colour: Dark greenish black to greenish blue
Solubility:
Environments:

Hydrothermal environments

Clinoclase is a rare secondary mineral in the oxidized zone of some arsenic-rich hydrothermal base-metal deposits. At the type locality, Wheal Gorland, Cornwall, England, clinoclase is associated with olivenite, liroconite and cornwallite. At the Clara Mine, Near Wolfach in the Black Forest, Germany, clinoclase is associated with olivenite, conichalcite, malachite and azurite, all on a baryte-rich matrix.
Common impurities: P

Clinoenstatite

Formula: Mg2Si2O6 inosilicate (chain silicate) pyroxene
Specific gravity:
Hardness: 5 to 6
Streak: White
Colour: Colourless, greenish yellow, yellowish brown, green-brown
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments:

Plutonic igneous environments

Alteration

forsterite and anorthite to clinoenstatite, diopside and spinel
2Mg2SiO4 + CaAl2Si2O8 ⇌ 2MgSiO3 + CaMgSi2O6 + MgAl2O4
The reaction can proceed in either direction, depending on the ambient conditions.

Common impurities: Ti,Al,Cr,Fe,Mn,Ca,Na

Clinohedrite

Formula: CaZn(SiO4).H2O
Nesosilicate (insular SiO4 groups)
Specific gravity: 3.33
Hardness: 5½
Streak: White
Colour: Colourless to white, pale amethystine
Solubility: Gelatinised in hydrochloric acid
Environments:

Metamorphic environments
Hydrothermal environments

At the type locality, Trotter mine, Franklin, New Jersey, USA, clinohedrite occurs in a hydrothermally altered, metamorphosed zinc-manganese-iron silicate-oxide orebody, with willemite, axinite, hancockite, roeblingite, hardystonite, esperite, datolite, bustamite, andradite, nasonite, glaucochroite, calcite, larsenite, hodgkinsonite and franklinite.
At the Christmas mine, Arizona, USA, clinohedrite occurs with stringhamite, kinoite and apophyllite.
Common impurities: Fe,Al,Mn,Mg

Clinohumite

Formula: Mg9(SiO4)4F2 nesosilicate (insular SiO4 groups)
Specific gravity: 3.17 to 3.35
Hardness: 6
Streak: White
Colour: Brown, yellow, white, orange, reddish brown.
Environments:

Metamorphic environments

Clinohumite is a product of contact metamorphism.
It may be found in dolostone, kimberlite, limestone and peridotite. Titanium is a minor constituent of clinohumite in most occurrences. Clinohumite is stable throughout the upper mantle to depths of at least 410 km.

Common impurities: Fe,Ti,Al,Mn,Ca,(OH)

Clinoptilolite

Formula:
Clinoptilolite-Ca: Ca3(Si30Al6)O72.20H2O
Clinoptilolite-K: K6(Si30Al6)O72.20H2O
Clinoptilolite-Na: Na6(Si30Al6)O72.20H2O

All are tectosilicates (framework silicates), zeolite group
Specific gravity: 2.1 to 2.2
Hardness: 3½ to 4
Streak: White
Colour: White, Reddish white, red
Environments:

Volcanic igneous environments

Clinoptilolite is most commonly formed as a devitrification product of silicic volcanic glass from tuff (consolidated pyroclastic rock). It also occurs in cavities in rhyolites, andesites, and basalts.

Clinozoisite

Formula: Ca2Al3[Si2O7][SiO4]O(OH) sorosilicate (Si2O7 groups) epidote group
Specific gravity:
Hardness: 7
Streak: Greyish white
Colour: Colourless, green, grey, light green, yellow-green, pink
Solubility: Insoluble in water, nitric and sulphuric acid; soluble in hydrochloric acid
Environments:

Metamorphic environments

Clinozoisite is a mineral of the amphibolite facies.

Alteration

amphibole, clinozoisite, chlorite, albite, ilmenite and quartz to garnet, omphacite, rutile and H2O
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + 2Ca2Al3[Si2o7][SiO4]O(OH) + Mg5Al(AlSi3O10)(OH)8 + 3NaAlSi3O8 + 4Fe2+Ti4+O3 + 3SiO2 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 6H2O In low-grade rocks relatively poor in calcite the garnet-omphacite association may be developed by the above reaction.

lawsonite and jadeite to clinozoisite, paragonite, quartz and H2O
4CaAl2(Si2O7)(OH)2.H2 + NaAlSi2O6 ⇌ 2Ca2Al3[Si2o7][SiO4]O(OH) + NaAl2(Si3Al)O10(OH)2 + SiO2 +6H2
Clinozoisite and paragonite may have been derived from lawsonite by the above reaction.

meionite (scapolite series) and H2O to clinozoisite and CO2
Ca4Al6O24(CO3) + H2O ⇌ 2Ca2Al3Si3O12(OH) + CO2

Common impurities: Ti,Fe,Mn,Mg

Cobaltarthurite

Formula: CoFe3+2(AsO4)2(OH)2.4H2O
Hydrated arsenate containing hydroxyl, arthurite group
Specific gravity: 3.22
Hardness: 3½ to 4
Streak: White to pale brown
Colour: Yellowish brown to straw yellow
Environments:

Hydrothermal environments

Cobaltarthurite is a secondary mineral.

At Khder, Bou Azzer, Morocco, cobaltarthurite occurs in cavities in lollingite ore associated with arseniosiderite, scorodite and karibibite.

At Oumlil-East, Bou Azzer, Morocco, cobaltarthurite occurs in vein rock associated with karibibite and parasymplesite.

At the type locality at the Dolores prospect in Murcia, Spain, cobaltarthurite occurs is associated with olivenite and arseniosiderite.

Coesite

Formula: SiO2 tectosilicate (framework silicate) Silica minerals stability diagram A high-pressure polymorph of quartz
Specific gravity: 2.92
Hardness: 7½ - 8
Streak: White
Colour: Colourless
Environments:

Metamorphic environments

Coesite may be found in eclogite and kimberlite.
It is a mineral of the blueschist and eclogite facies.

Alteration

Coesite is a high pressure polymorph of quartz. With increasing pressure, At 800oC alpha quartz alters to coesite at about 30 kbar pressure, then coesite alters to stishovite at about 90 kbar.
alpha quartz, beta quartz and coesite can co-exist at a point where the temperature is about 1,360oC and the pressure 34 kbar.
beta quartz and coesite can co-exist in equilibrium with the silica melt at a point where the temperature is about 2,410oC and the pressure 45 kbar.
With further increase in pressure and temerature, coesite can continue to exist up to about 2,770oC and 110 kbar pressure, at which point coesite, stishovite and the silica melt are in equilibrium.

Common impurities: Al,Fe,Na

Colemanite

Formula: CaB3O4(OH)3.H2O borate
Specific gravity: 2.4
Hardness: 4½
Streak: White
Colour: Colourless, white
Solubility: Slightly soluble in water
Environments:

Sedimentary environments

Colemanite occurs in borax lake bed deposits and sediments, in arid alkali environments. Ulexite and borax are usually associated, and colemanite is believed to have originated by their alteration.

Columbite

There are three columbites:
columbite-(Fe): Fe2+Nb2O6,
columbite-(Mg): MgNb2O6, and
columbite-(Mn): Mn2+Nb2O6
All of these are multiple oxides containing niobium, and members of the columbite group

Specific gravity: 5.3 - 8.1
Hardness: 6
Streak: Brown to black
Colour: Brownish black to black
Solubility: Insoluble in hydrochloric and nitric acid; slightly soluble in sulphuric acid
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites

Columbite occurs in granitic rocks and pegmatites, associated with quartz, feldspars, mica, tourmaline, beryl, spodumene, cassiterite, hübnerite-ferberite, microlite and monazite.

Conichalcite

Formula: CaCu(AsO4)(OH)
Anhydrous arsenate with hydroxyl, adelite-descloizite group, adelite subgroup. Forms a series with austinite, with cobaltaustinite, with duftite and with tangeite.
Specific gravity: 4.33
Hardness: 4½
Streak: Green
Colour: Green, yellow-green, greenish yellow; light green to yellowish green in transmitted light.
Solubility: Easily soluble in hydrochloric and nitric acids
Environments:

Hydrothermal environments

Conichalcite is a secondary mineral found in the oxidised zones of copper deposits, typically an alteration product of enargite, associated with goethite, austinite, olivenite, clinoclase, libethenite, chenevixite, brochantite, malachite, azurite and jarosite.

Localities

France

At Chessy-les-Mines, Auvergne-Rhône-Alpes, France, conichalcite occurs in cavities in sandstone associated with tyrolite.

At Valzergues, Occitanie, France, conichalcite is associated with quartz, goethite, monazite-(Ce), and agardite-(Y).

At the Cap Garonne Mine, Provence-Alpes-Côte d'Azur, France, conichalcite is associated with cerussite, olivenite, beudantite, and mimetite.

Germany
At the Clara Mine, Baden-Württemberg, Germany, conichalcite is associated with chrysocolla and cuprite.

Italy

At the San Pietro mine, Sardinia, Italy, conichalcite is associated with calcite.

Morocco

At Bou Azzer, Drâa-Tafilalet Region, Morocco, conichalcite is associated with roselite and roselite-β. At the Méchoui deposit it is associated with erythrite. At the Ightem mine, it is associated with malachite, azurite, powellite and talmessite. In the Oumlil-East open pit it is associated with chrysocolla, and at Ambed it occurs with quartz. At the Aghbar open pit conichalcite commonly encrusts grains of chalcopyrite and chalcocite, and it has also been found associated with dioptase and chrysocolla.

Namibia

At Tsumeb, Namimia, conichalcite is most commonly associated with adamite, but it is also rarely associated with smithsonite, malachite, duftite, willemite, and olivenite.

Spain

At the Delfina Mine, Asturias, Spain, conichalcite is associated with azurite, cobaltarthurite, tyrolite or smithsonite.

USA

At the Bristol mine, Lincoln County, Nevada, USA, conichalcite is associated with jarosite, malachite, chrysocolla and melanochalcite.

Common impurities: Mg,P,V,Zn

Connellite

Formula: Cu36(SO4)(OH)62Cl8.6H2O
Hydrated sulphate containing hydroxyl and halogen, connellite-buttgenbachite Series.
Specific gravity: 3.36
Hardness: 3
Streak: Pale greenish blue
Colour: Azure blue
Solubility: Insoluble in water, soluble in acids and in NH4OH. Easily fusible.

Environments:

Hydrothermal environments

Connellite is an uncommon secondary mineral in the oxidized portions of copper deposits, associated with cuprite, spangolite, atacamite, botallackite, langite, malachite and azurite.
At the Roughton Gill Mines, Cumbria, England, connellite is often found where copper veins oxidise in saline environments, and is also sometimes found in the supergene oxidation zones of base metal orebodies; in these assemblages it is commonly associated with cuprite.
At the Gallagher mine dumps, Cochise County, Arizona, USA, connellite is associated with anglesite, botallackite, bromian chlorargyrite, cerussite and chrysocolla.

Cookeite

Formula: (Al,Li)3Al2(Si,Al)4O10(OH)8 phyllosilicate (sheet silicate) chlorite group
Specific gravity: 2.58 to 2.69
Hardness: 2½ to 3½
Streak: White
Colour: White, yellowish green, pink, brown. Colourless when pure.
Solubility: Insoluble in common acids; soluble in HF
Environments:

Pegmatites
Hydrothermal environments

Cookeite occurs as late stage mineralisation in gem-pocket-bearing granite pegmatites associated with cleavelandite, elbaite, lepidolite and spodumene. It has also been found as pseudomorphs of spodumene, petalite and elbaite. Cookeite also occurs in some simple quartz-crystal lined veins, and in hydrothermally altered sedimentary rocks with kaolinite, diaspore, böhmite, illite, sandstone and bauxite.

Alteration

Cookeite has been synthesised at 260 to 480oC, 1-14 kbar pressure.
It can be formed by the alteration of kaolinite and diaspore by lithium-bearing solutions, releasing quartz.

Common impurities: Fe,Mn,Mg,Ca,Na,K

Copper

Formula: Cu native element
Specific gravity: 8.93
Hardness: 2½ to 3
Streak: Copper red
Colour: Copper red
Solubility: Slightly soluble in hydrochloric acid; moderately soluble in sulphuric acid; readily soluble in nitric acid
Environments:

Volcanic igneous environments
Hydrothermal environments
Basaltic cavities

Small amounts of native copper have been found at many localities in the oxidation zones of copper deposits, associated with cuprite, malachite and azurite. These minerals may be carried in solution down to the enriched zone, where secondary copper may be redeposited. Deposits of native copper are also found in cavities in basalt lavas, resulting from the reaction of hydrothermal solutions with iron oxide minerals, and the richest source of copper in the world is the basalt lava flows of the Keweenaw peninsula, USA.

Cordierite

Formula: Mg2Al4Si5O18 cyclosilicate (ring silicate)
Specific gravity: 2.5 to 2.8
Hardness: 7 to 7½
Streak: White
Colour: Grey, blue to violet, yellow to brown, greenish, also colourless
Solubility: Slightly soluble in hydrochloric acid
Environments:

Plutonic igneous environments
Metamorphic environments (typical)

Cordierite is a common constituent of contact and regionally metamorphosed argillaceous (clay-rich) rocks. It is especially common in hornfels, and it is also found in regionally metamorphosed cordierite-garnet- sillimanite gneiss and schist.
Cordierite may be found in granite, gabbro, phyllite, schist and gneiss. It is also found in river gravel.
Common associations are sillimanite and spinel, or spinel, plagioclase feldspar and orthopyroxene. Cordierite associated with anthophyllite has been described from several localities.
Cordierite is a mineral of the hornblende-hornfels, pyroxene-hornfels, greenschist, amphibolite and granulite facies.

Alteration

chlorite, muscovite and quartz to biotite, Fe-rich cordierite and H2O
(Mg,Fe2+)5Al(AlSi3O10)(OH)8 + KAl2(AlSi3O10)(OH)2 + 2SiO2 → K(Mg,Fe2+)3(AlSi3O10)(OH)2 + (Mg,Fe2+)2Al4Si5O18 + 4H2O
This reaction ocurs when the metamorphic grade increases

chlorite and quartz to enstatite-ferrosilite, Fe-rich cordierite and H2O
(Mg,Fe2+)4Al4Si2O10(OH)8 + 5SiO2 → 2(Mg,Fe2+)SiO3 + (Mg,Fe2+)2Al4Si5O18 + 4H2O
Enstatite-ferrosilite also occurs in medium grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content according to the above equation.

Fe rich cordierite and diopside- hedenbergite to enstatite- ferrosilite, anorthite and quartz
(Mg,Fe)2 Al4Si5O18 + 2Ca(Mg,Fe)Si2O6 = 4(Mg,Fe2+)SiO3 + 2Ca(Al2Si2O8) + SiO2

enstatite and corundum to cordierite and spinel
5Mg2Si2O6 + 10Al2O3 ⇌ 2Mg2Al4Si5O18 + 6MgAl2O4
At 6 kbar pressure the equilibrium temperature is about 715oC (amphibolite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

enstatite, kyanite and quartz to cordierite
Mg2Si2O6 + 2Al2OSiO4 + SiO2 ⇌ Mg2Al4Si5O18
At 6 kbar pressure the equilibrium temperature is about 475oC (greenschist facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

enstatite and spinel to forsterite and cordierite
5Mg2Si2O6 + 2MgAl2O4 ⇌ 5Mg2SiO4 + Mg2Al4Si5O18
At 4 kbar pressure the equilibrium temperature is about 715oC (amphibolite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

enstatite-ferrosilite and andalusite to Fe-rich cordierite and spinel- hercynite
5(Mg,Fe2+)SiO3 + 5 Al2SiO5 → 2(Mg,Fe2+)2Al4Si5O18 + (Mg,Fe2+)Al2O4
In medium-grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content, in an SiO2 deficient environment the association of andalusite with enstatite-ferrosilite is excluded by the above reaction.

enstatite-ferrosilite, andalusite and quartz to Fe-rich cordierite
2(Mg,Fe2+)SiO3 + 2Al2SiO5 + SiO2 → (Mg,Fe2+)2Al4Si5O18
In medium-grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content, the association of andalusite with enstatite-ferrosilite is excluded by the above reaction.

forsterite, kyanite and quartz to cordierite
Mg2SiO4 + 2Al2OSiO4 + 2SiO2 ⇌ Mg2Al4Si5O18
At 6 kbar pressure the equilibrium temperature is about 400oC (greenschist facies).

gedrite-ferro-gedrite and quartz to enstatite-ferrosilite, Fe-rich cordierite and H2O
(Mg,Fe2+)5Al4Si6O22(OH)2 + 2Si2 → 3(Mg,Fe2+)SiO3 + (Mg,Fe2+)2Al4Si5O18 + H2O In the pyroxene-hornfels facies enstatite-ferrosilite may develop from gedrite-ferro-gedrite according to the above reaction.

kyanite and enstatite to cordierite and corundum
3Al2O(SiO4) + Mg2Si2O6 ⇌ Mg2Al4Si5O18 + Al2O3
The equilibrium temperature for this reaction at 6 kbar pressure is about 520oC (amphibolite facies), with equilibrium to the right at higher temperatures, and to the left at lower temperatures.

talc and kyanite to cordierite, corundum and H2O
2Mg3Si4O10(OH)2 + 7Al2OSiO4 ⇌ 3Mg2Al4Si5O18 + Al2O3 + 2H2O

Common impurities: Mn,Fe,Ti,Ca,Na,K

Corkite

Formula: PbFe3+3(SO4)(PO4)(OH)6
Compound phosphate
Specific gravity: 4.295
Hardness: 3½ to 4½
Colour: Brown to light yellowish brown, pale yellow, yellowish green to dark green
Solubility: Readily soluble in warm hydrochloric acid
Occurrence: Corkite is an uncommon secondary mineral formed at low temperatures or by weathering in oxidised hydrothermal base-metal deposits. At the type locality, the Glandore Mine, Ireland, it is found in a manganese-copper vein deposit associated with manganese oxides, malachite, goethite, cuprite and baryte.

Cornubite

Formula: Cu5(AsO4)2(OH)4
Anhydrous arsenate containing hydroxyl, dimorph of cornwallite
Specific gravity: 4.64
Hardness: 4
Streak: Pale green
Colour: Apple green to dark green
Environments:

Hydrothermal environments

Cornubite is a rare secondary mineral in oxidised copper deposits. Near Reichenbach in the Oderwald, Germany, cornubite occurs in a silicified quartz vein.

At the type locality, Wheal Carpenter, Cornwall, England cornubite occurs in copper-tin-silver bearing hydrothermal veins, associated with cornwallite, chalcophyllite, olivenite, liroconite, chenevixite, clinoclase, pseudomalachite, bayldonite, parnauite, tyrolite, azurite, malachite, cuprite, chrysocolla, quartz and obvenite.

At the San Rafael mine, Nye county, Nevada, USA, cornubite has been found with olivenite and strashimirite.

At Bou Azzer, Morocco cornubite has been found in quartz cavities together with scorodite.

Cornwallite

Formula: Cu5(AsO4)2(OH)4
Anhydrous arsenate containing hydroxyl, dimorph of cornubite
Forms a series with pseudomalachite
Specific gravity: 4.52
Hardness: 4½
Streak: Apple green
Colour: Verdigis green, blackish-green, emerald-green; emerald-green in transmitted light.
Solubility: Decomposed in oils containing As2S3. Soluble in nitric acid.
Environments:

Hydrothermal environments

Cornwallite is a rare secondary mineral formed by the oxidation of ore containing both copper and arsenic (e.g, tennantite). At the type locality, Wheal Carpenter, Cornwall, England it occurs in copper bearing sulphide veins associated with olivenite, cornubite, arthurite, clinoclase, chalcophyllite, strashimirite, lavendulan, tyrolite, spangolite, austinite, conichalcite, brochantite, azurite and malachite.

Two specimens of cornwallite have been reported from the Kintore open cut, Broken Hill, New South Wales, Australia. One occurs on globular conichalcite, and the other shows all the stages of replacement by globular chrysocolla.

At the Telfer gold mine, Western Australia, cornwallite is associated with chalcocite, chrysocolla, agardite, malachite and cornubite.

At the San Rafael mine, Nye county, Nevada, USA, cornwallite has been found with olivenite and mimetite.

At Short Grain, Caldbeck Fells, Cumbria, England cornwallite occurs with chrysocolla and occasionally with supergene baryte in cavities in quartz or coating the exterior of blocks of altered veinstone.

Common impurities: P

Coronadite

Formula: Pb(Mn4+6Mn3+2)O16 multiple oxide, cryptomelane group
Specific gravity: 5.44
Hardness: 4½ to 5
Streak: Brownish black
Colour: Dark grey to black
Environments:

Sedimentary environments
Metamorphic environments
Hydrothermal environments
Hot springs

Coronadite occurs as a primary mineral in hydrothermal veins or from hot springs, and it is of secondary origin in oxidized zones above manganese deposits and bedded sedimentary rocks. Hollandite, pyrolusite and other manganese oxides are common associates.
Common impurities: Fe,Al,H2O

Corundum

Formula: Al2O3 oxide
Specific gravity: 3.98 to 4.1
Hardness: 9
Streak: White
Colour: Colourless, blue, red, pink, yellow, brown
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Plutonic igneous environments
Pegmatites
Sedimentary environments
Placer deposits
Metamorphic environments

Corundum is common as an accessory mineral in contact and regionally metamorphosed rocks, such as limestone, mica-schist and gneiss. It is also found as an original constituent of silica deficient igneous rocks such as syenite and nepheline syenite, and in pegmatites. It may be found in large masses in the zone separating peridotite from the adjacent country rock. It is found frequently as a detrital material in sediments, preserved through its hardness and chemical inertness. It also may be found in eclogite and gneiss.
Commonly associated minerals are chlorite, mica, olivine, serpentine, magnetite, spinel, kyanite and diaspore. Quartz never occurs with corundum.
It is a mineral of the albite-epidote-hornfels, hornblende-hornfels greenschist, amphibolite, eclogite and granulite facies.

Alteration

anorthite and CO2 to meionite (scapolite series), corundum and quartz
4Ca(Al2Si2O8) + CO2 ⇌ Ca4Al6O24(CO3) + Al2O3 + 2SiO2

corundum and forsterite to spinel and enstatite
2Al2O3 + 2Mg2SiO4 ⇌ 2MgAl2O4 + Mg2Si2O6
At 10 kbar pressure the equilibrium temperature is about 570oC (amphibolite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

diaspore to corundum and H2O
2AlO(OH) ⇌ Al2O3 + H2O
High temperature favours the forward reaction. At 1 kbar pressure the reaction occurs at about 320oC (albite-epidote-hornfels facies), and at 10 kbar it occurs at about 490oC (greenschist facies).

enstatite and corundum to cordierite and spinel
5Mg2Si2O6 + 10Al2O3 ⇌ 2Mg2Al4Si5O18 + 6MgAl2O4
At 6 kbar pressure the equilibrium temperature is about 715oC (amphibolite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

enstatite and corundum to pyrope
3Mg2Si2O6 + 2Al2O3 ⇌ 2Mg3Al2(SiO4)3
At 14 kbar pressure the equilibrium temperature is about 810oC (eclogite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

grossular and corundum to anorthite and gehlenite
2Ca3Al2(SiO4)3 + Al2O3 ⇌ CaAl2Si2O8 + Ca2Al2SiO7
The equilibrium temperature for this reaction at 5 kbar pressure is about 950oC At 4.3 kbar pressure the equilibrium temperature is about 890oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

kyanite and enstatite to cordierite and corundum
3Al2O(SiO4) + Mg2Si2O6 ⇌ Mg2Al4Si5O18 + Al2O3
The equilibrium temperature for this reaction at 6 kbar pressure is about 520oC (amphibolite facies), with equilibrium to the right at higher temperatures, and to the left at lower temperatures.

kyanite and zoisite to anorthite, corundum and H2O
2Al2O(SiO4) + 2Ca2Al3[Si2O7][SiO4]O(OH) ⇌ 4CaAl2Si2O8 + Al2O3 + H2O
The equilibrium temperature for this reaction at 5 kbar pressure is 480oC (greenschist facies), and at 10 kbar it is about 720oC (amphibolite facies). The equilibrium is to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and corundum to zoisite, kyanite and H2O
4CaAl2(Si2O7)(OH)2.H2 + Al2O3 ⇌ 2Ca2Al3[Si2O7][SiO4}O(OH) + 2Al2OSiO4 + 7H2O
The equilibrium temperature for this reaction at 15 kbar pressure is about 570oC (eclogite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite to corundum, anorthite and H2O
CaAl2(Al2Si2O10)(OH)2 ⇌ Al2O3 + Ca(Al2Si2O8)
The equilibrium temperature for this reaction at 6 kbar pressure is about 610oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite to corundum, zoisite, kyanite and H2O
4CaAl2(Al2Si2O10)(OH)2 ⇌ 3Al2O3 + 2Ca2Al3[Si2O7][SiO4]O(OH) + 2Al2OSiO4 + 3H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 650oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

muscovite to corundum, K-feldspar and H2O
KAl2(AlSi3O10)(OH)2 ⇌ Al2O3 + K(AlSi3O8) + H2O
This reaction takes place above temperatures ranging from 600oC at atmospheric pressure (hornblende-hornfels facies) to about 720oC at pressure above 4 kbar (amphibolite facies).

staurolite, annite and O2 to hercynite, magnetite, muscovite, corundum, SiO2 and H2O
2Fe2+2Al9Si4O23(OH) + KFe2+3 (AlSi3O10)(OH)2 +2O2 → 4Fe2+Al2O4 + Fe2+Fe3+2O4 + KAl2 (AlSi3O10)OH)2 + 4Al2O3 + 8SiO2 + 2H2O

talc and kyanite to cordierite, corundum and H2O
2Mg3Si4O10(OH)2 + 7Al2OSiO4 ⇌ 3Mg2Al4Si5O18 + Al2O3 + 2H2O

zoisite to anorthite, grossular, corundum and H2O
6Ca2Al3[Si2O7][SiO4]O(OH) ⇌ 6CaAl2Si2O8 + 2Ca3Al2Si3O12 + Al2O3 + 3H2O
The equilibrium temperature for this reaction at 6 kbar pressure is about 760oC, and at 10 kbar it is about 950oC (granulite facies). For any given pressure, the reaction goes to the right at higher temperatures, and to the left at lower temperatures.

Covellite

Formula: CuS sulphide
Specific gravity: 4.68
Hardness: 1½ to 2
Streak: Blue-black
Colour: Blue-black
Solubility: Slightly soluble in hydrochloric acid and sulphuric acid; moderately soluble in nitric acid
Environments:

Metamorphic environments
Hydrothermal environments
Volcanic sublimates (very rarely)

Covellite is not an abundant mineral; it is usually found as a secondary copper mineral in copper deposits, more rarely as a primary mineral, and only very rarely as a volcanic sublimate. It is found in the enrichment zone of most copper deposits, usually as a coating, associated with other copper minerals, principally chalcocite, chalcopyrite, bornite and enargite, and is derived from them by alteration.

Alteration

Covellite may occur as an alteration product of chalcopyrite.

Oxidation of pyrite forms ferrous (divalent) sulphate and sulphuric acid:
pyrite + oxygen + water → ferric sulphate + sulphuric acid
FeS2 + 7O + H2O → FeSO4 + H2SO4
The ferrous (divalent) sulphate readily oxidizes to ferric (trivalent) sulphate and ferric hydroxide:
ferrous sulphate + oxygen + water → ferric sulphate + ferric hydroxide
6FeSO4 + 3O + 3H2O → 2Fe2(SO4)3 + 2Fe(OH)3
Ferric sulfate is a strong oxidizing agent and attacks both chalcocite and covellite.

chalcocite and ferrous sulphate to copper sulphate, ferrous sulphate and covellite
Cu2S + Fe2(SO4)3 → CuSO4 + 2FeSO4 + CuS

covellite and ferric sulphate to ferrous sulphate, copper sulphate and sulphur
CuS + Fe2(SO4)3 → 2FeSO4 + CuSO4 + S
Covellite is further oxidised according to the above reaction to form sulphur.

Common impurities: Fe,Se,Ag,Pb

Crandallite

Formula: CaAl3(PO4)(PO3OH)(OH)6 hydrated phosphate containing hydroxyl
Specific gravity: 2.92
Hardness: 5
Streak: White
Colour: Yellow, white, gray; colourless in transmitted light.
Solubility: Soluble with difficulty in acids.
Environments:

Pegmatites
Sedimentary environments

Crandallite is a secondary mineral that occurs in iron-rich, silica-poor phosphate deposits and as an alteration product in pegmatites.

Alteration

Crandallite may be found as a pseudomorph after gordonite.

Common impurities: Sr and Ba substituting for Ca and Fe3+ for Al.

Localities

USA

Crandallite at the Bone Valley Formation, Florida, is associated with clay, millisite and wavellite.

At the Brooklyn Mine, Utah, it is associated with quartz and baryte.

At fairfield, Utah, crandallite is associated with millisite, wardite, variscite, gordonite, englishite, montgomeryite, overite, kolbeckite and apatite.

Creaseyite

Formula: Cu2Pb2Fe3+2Si5O17.6H2O
Unclassified silicate
Specific gravity: 4.1
Hardness: 2½
Streak: Pale green
Colour: Yellow-green
Solubility: Decomposed by hot dilute hydrochloric and nitric acid, yielding a silica sponge; fuses to a rusty brown slag.
Environments:

Hydrothermal environments

Creaseyite is found in the oxidised zones of copper deposits.
At Caborca, Sonora, Mexico, creaseyite is mostly replaced by chrysocolla.
At the Gallagher Vanadium property and Manila mine, Cochise county, Arizona, USA, creaseyite is associated with cerussite, and occurs as inclusions in cerussite and calcite.
At Tiger, Gila county, Arizona, USA, creaseyite occurs in the oxidised zone of a base-metal deposit, in andesite breccia loosely cemented with iron oxides and wulfenite, and associated with mimetite, dioptase, fluorite, willemite, wulfenite, descloizite and murdochite.
At the Potter-Cramer property, Maricopa county, Arizona, USA, creaseyite is associated with ajoite and fluorite.
At Wickenburg, Maricopa county, Arizona, USA, creaseyite occurs with fluorite and ajoite.
At the Mammoth mine, Pinal county, Arizona, USA, creaseyite occurs in oxidised zones with wulfenite, willemite and mimetite.

Common impurities: Al,Zn

Cristobalite

Formula: SiO2 tectosilicate (framework silicate) Silica minerals stability diagram
Cristobalite is a polymorph of quartz that exists both as α and as β phases. β-cristobalite is the stable form of SiO2 from 1,460oC to the melting point, 1,728oC. It exists as a metastable phase below 1,470oC because the transition to tridymite proceeds very slowly. The transformation from β to α-cristobalite occurs at 268oC for pure cristobalite, but may be as low as 175oC if a high level of impurities exists.
Specific gravity: 2.2 to 2.33
Hardness: 6½
Streak: White
Colour: Colorless, white, also blue grey, brown, grey, yellow
Environments:

Volcanic igneous environments
Metamorphic environments

Cristobalite occurs both as α and as β forms as a component of opal. Crystalline material occurs in silica-rich volcanic rocks. It is characteristic in vesicles in rhyolite, andesite and trachyte, where it is associated with tridymite, quartz, sanidine, pyroxene, fayalite and magnetite, and also in basalt. It is also found in thermally metamorphosed sandstone.

Alteration

At atmospheric pressure, with increasing temperature tridymite alters to cristobalite at 1,470oC, and cristobalite melts at 1,705oC. Tridymite, cristobalite and beta quartz can co-exist in equilibrium at a point with temperature about 1,400 oC and pressure 30 kbar.

Common impurities: Fe,Ca,Al,K,Na,Ti,Mn,Mg,P

Crocoite

Formula: Pb(CrO4) chromate
Specific gravity: 5.9 - 6.0
Hardness: 2½; to 3
Streak: Orange
Colour: Red to orange
Solubility: Slightly soluble in hydrochloric, sulphuric and nitric acid
Environments:

Hydrothermal environments

Crocoite is a rare mineral found in the oxidation zone of high temperature lead deposits in those regions where lead veins have traversed rocks containing chromite. Associated with pyromorphite, cerussite and wulfenite.

Common impurities: Zn,S

Cronstedtite

Formula:(Fe2+,Fe3+)3(Si,Fe3+)2O5(OH)4 pyllosilicate (sheet silicate) serpentine group

Formula:
Specific gravity:
Hardness: 3½
Streak: Dark olive green
Colour: Black, dark brown-black, green-black
Environments:

Hydrothermal environments

Cronstedtite is a low temperature hydrothermal product in ore veins, commonly associated with clinochlore, pyrite, quartz, siderite and sphalerite

Alteration

fayalite, H2O and O2 to cronstedtite and magnetite
6Fe2+2(SiO4) + 6H2O + ½O2 = 3Fe3Si2O5(OH)4 + Fe2+Fe3+2O4

Common impurities: Al,Ca

Cryptomelane

Formula: K(Mn4+7Mn3+)O16
Multiple oxide, cryptomelane group
Specific gravity: 4.3
Hardness: 5 to 6½
Streak: Brownish black
Colour: Grey to black (Dana)
Environments:

Hydrothermal environments

Cryptomelane is the commonest of the hard, black, fine-grained manganese oxides formerly called psilomelane. It is a low-temperature supergene mineral, widespread in oxidised manganese deposits as open-space fillings or replacing primary manganese-bearing minerals. It is commonly replaced by other secondary manganese minerals, and associated with pyrolusite, nsutite, braunite, chalcophanite, manganite and other manganese oxides.
At Burdell Gill, Caldbeck Fells, Cumbria, England, there is some evidence that cryptomelane has pseudomorphed a rhombohedral mineral, possibly ankerite or siderite.

Cubanite

Formula: CuFe2S3
Specific gravity: 4.0 to 4.2
Hardness: 3½
Streak: Grey-black
Colour: Brass to bronze-yellow
Magnetic

Cummingtonite

Formula: ☐Mg2Mg5Si8O22(OH)2 inosilicate (chain silicate) amphibole
Cummingtonite is a dimorph of anthophyllite.
Hardness: 5 to 6
Streak: not determined
Colour: Translucent dark green, brown, grey, colourless
Environments:

Metamorphic environments

Cummingtonite is found in both contact and regional metamorphic rocks

Alteration

cummingtonite-grunerite and H2O to serpentine and quartz
6(Fe,Mg)7Si8O22(OH)2 + 22H2O ⇌ 7(Fe,Mg)6Si4O10(OH)8 + 20SiO2

cummingtonite-grunerite and olivine to enstatite-ferrosilite and H2O
(Fe,Mg)7Si8O22(OH)2 + (Mg,Fe)2SiO4 ⇌ 9(Mg,Fe2+)SiO3 + H2O

enstatite and H2O to forsterite and cummingtonite
9MgSiO3 + H2O = Mg2SiO4 + Mg2Mg5Si8O22(OH)2
Cummingtonite may be formed by retrograde metamorphism according to the above reaction.

enstatite-ferrosilite, SiO2 and H2O to cummingtonite-grunerite
7(Mg,Fe2+)SiO3 + SiO2 + H2O ⇌ (Fe,Mg)7Si8O22(OH)2

Common impurities: Mn,Ca,Al,Ti,Na,K

Cuprite

Formula: Cu2O oxide
Specific gravity: 6.15
Hardness: 3½ to 4
Streak: Brownish red
Colour: Red
Solubility: Moderately soluble in hydrochloric acid; slightly soluble in sulphuric and nitric acid
Environments:

Hydrothermal environments

Cuprite is a secondary mineral found in the oxidation portions of high temperature copper deposits, associated with limonite and secondary copper minerals such as copper, malachite, azurite and chrysocolla.
It may be found as an oxidation product coating native copper, or as an alteration product of chalcopyrite. Cuprite crystals are found rimmed with green malachite at the Cotopaxi Mine, Colorado, overgrown with goethite at the Chino Mine, New Mexico and pseudomorphed by shattuckite at the Mashamba West Mine, Democratic Republic of Congo.

Cyanotrichite

Formula: Cu4Al2(SO4)(OH)12(H2O)2 sulphate
Specific gravity: 3.7 to 3.9
Hardness: 3½ to 4
Streak: Blue
Colour: Sky blue
Solubility: Moderately soluble in hydrochloric, sulphuric and nitric acid
Environments:

Hydrothermal environments

Cyanotrichite is a secondary copper mineral found sparsely in the oxidation zones of hypothermal (high temperature) copper-bearing ore bodies rich in aluminium and sulphate. Associated minerals include brochantite, spangolite, chalcophyllite, olivenite, tyrolite, parnauite, azurite and malachite.

Cymrite

Formula: Ba(Si,Al)4(O,OH)8.H2O
Unclassified silicate
Specific gravity: 3.41
Hardness: 2 to 3
Streak: White
Colour: White, colourless, green or brown. Green and brown colours are caused by inclusions of alteration products.
Solubility: Slightly soluble in acids
Environments:

Metamorphic environments

Cymrite occurs in bedded manganese ore deposits due to low to medium grade metamorphism, amphibolite facies. It is stable at high pressure.

At the Andros Islad, Greece, cymrite is a product of high-pressure metamorphism of manganese-rich rocks.

At Långban, Sweden, cymrite is associated with hyalotekite, banalsite, hyalophane, hedyphane and manganoan biotite.

At the Benallt mine, Wales, UK, cymrite occurs in veinlets cutting hydrothermal manganese silicate ore, associated with ganophyllite.

At Ruby Creek in the Cosmos Hills, Brooks Range, Alaska, USA, cymrite occurs as minute crystals randomly scattered throughout a fine-grained dolomitic and sideritic matrix. The host-rock was originally a normal dolomite of marine origin, but it is now mineralised and contains pyrite, chalcopyrite, bornite, chalcocite, sphalerite, galena and cymrite, together with small amounts of chlorite, fluorite, pyrrhotite, dickite, and bementite. Cymrite is observed in contact with one or more of the following minerals: dolomite, siderite, ankerite, pyrite, fluorite, quartz and chlorite.

At San Benito county, California, USA, cymrite occurs in jadeite greywacke (a dark coarse-grained sandstone containing more than 15 per cent clay) near the contact of an intrusive ultramafic rock, associated with calcite, albite and lawsonite.

Alteration

hydroxyl-poor cymrite to celsian and H2O
BaSi2Al2O8.H2O ⇌ Ba(Al2Si2O8) + H2O
Cymrite alters to celsian by dehydration.

Common impurities: Ti,Fe,Mn,Na,K

Dachiardite

Dachiardite is a series between three minerals:
Dachiardite-Ca: Ca2(Si20Al4)O48.13H2O
Dachiardite-K: K4(Si20Al4)O48.13H2O
Dachiardite-Na: Na4(Si20Al4)O48.13H2O
These minerals are tectosilicates (framework silicates), zeolite group
Specific gravity: 2.14 to 2.21
Hardness: 4 to 4½
Streak: White
Colour: Colourless, white, pink, orange-red
Solubility: Decomposed by common acids
Environments:

Volcanic igneous environments
Pegmatites
Hydrothermal environments


Dachiardite is a hydrothermal zeolite that generally occurs in silica-rich environments, in late stages of pegmatites and in Si-rich volcanic rocks, but also in basalt and in hydrothermally altered tuffaceous sediments. It may be associated with mordenite, ferrierite and heulandite, which, like dachiardite, are all zeolites. At Yellowstone Park drill holes show temperatures of formation of 100 to 200oC.

Danburite

Formula: CaB2Si2O8 tectosilicate (framework silicate)
Specific gravity: 2.9 to 3.0
Hardness: 7 to 7½
Streak: White
Colour: Colourless, yellowish to dark brown, pink
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Plutonic igneous environments
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Danburite occurs in hypothermal (high temperature) veins, where it is associated with quartz, cassiterite, fluorite and orthoclase, and in contact metamorphic rocks, where it is associated with andradite, wollastonite and sulphides.
Danburite occurs in granite and metamorphosed carbonates and evaporites, in skarn, in marine salt deposits and in alpine crevices.

Common impurities:Fe,Mn,Al,Mg,Sr,Na

Datolite

Formula: CaB(SiO4)(OH) nesosilicate (insular SiO4 groups)
Specific gravity: 2.9 to 3.0
Hardness: 5 to 5½
Streak: White
Colour: Colourless, white, yellow, greenish, seldom grey, reddish
Solubility: Slightly soluble in hydrochloric acid

Environments:

Metamorphic environments
Hydrothermal environments
Basaltic cavities

Datolite is a secondary mineral usually found in cavities in basalt lavas and similar rocks, associated with zeolites, prehnite, apophyllite and calcite. It also occurs in limestone skarn, serpentinite, schist, and ore veins.

Common impurities: Mn,Mg,Al,Fe

Dawsonite

Formula: NaAl(CO3)(OH)2 anhydrous carbonate containing hydroxyl
Specific gravity: 2.44
Hardness: 3
Streak: White
Colour: Colourless, white
Solubility: Soluble in acids with effervescence
Environments

Hydrothermal environments

Dawsonite is a low temperature hydrothermal carbonate formed decomposing aluminous silicates.

Localities

Algeria

In Tenes, Chlef Province, it occurs with baryte.

Canada

At McGill University campus, Quebec, Dawsonite is found as coatings on joint surfaces of a feldspar dyke associated with calcite, dolomite, pyrite, galena and manganese oxides.

Germany

In Solingen, North Rhine-Westphalia, it occurs in veins associated with late Tertiary basalt.

Italy

At Santa Fiora, Tuscany, dawsonite is associated with calcite, dolomite, pyrite, fluorite and cinnabar.

Descloizite

Formula: PbZn(VO4)(OH) anhydrous vanadate containing hydroxyl
Specific gravity: 6.2
Hardness: 3 to 3½
Streak: Orange to brownish-red
Colour: Brownish red, red-orange, reddish brown to blackish brown, nearly black
Solubility: Readily soluble in acids
Environments

Hydrothermal environments

Descloizite is a secondary mineral often found in the oxidation zones of metal ore deposits in association with mottramite in ore bodies containing vanadinite, pyromorphite, mimetite and cerussite. It has been found as pseudomorphs after vanadinite.

Localities

Namibia

At Berg Aukas Mine and at Tsumeb, descloizite occure with mottramite in sandy pockets in limestone and dolomite.

USA

At the Mammoth Mine, Arizona, descloizite occurs with mottramite

Common impurities: Cu

Devilline

Formula:CaCu4(SO4)2(OH)6.3H2O
Hydrated sulphate containing hydroxyl, devilline group
Specific gravity: 3.13
Hardness: 2½
Streak: Light green
Colour: Dark emerald green to bluish green
Solubility: Insoluble in water and concentrated sulphuric acid, soluble in nitric acid
Environments

Hydrothermal environments

Devilline is an uncommon secondary mineral in the oxidised portions of copper sulphide deposits; it may be of post-mining origin in dumps and on timbers. Associations: langite, antlerite, brochantite, posnjakite, linarite, malachite, azurite and gypsum.
At Vezzani, Corsica, France, devilline occurs in stalctites with spangolite.
At Spania Dolina, Slovakia, devilline occurs with gypsum, azurite and malachite.
At the Tynebottom mine, Cumbria, England, devilline is intergrown with serpierite, and sometimes surrounded by brochantite.
At the Gallagher Vanadium property and Manila mine, Cochise county, Arizona, USA, devilline is associated with gypsum and brochantite.

Diaboleite

Formula: CuPb2Cl2(OH)4 hydroxylhalide

Diamond

Formula: C native element
Specific gravity: 3.5 to 3.53
Hardness: 10
Streak: none
Colour: Colourless, yellow, green, pink, blue, black
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Plutonic igneous environments
Placers

Most commonly diamond is found as placers in alluvial deposits where it accumulates because of its inert chemical nature, its great hardness (it is the hardest natural substance known) and its fairly high specific gravity. The rock in which it is found in situ is kimberlite. It is formed deep in the mantle, and is only brought to the surface via kimberlite pipes. It is also found in alluvial deposits, along with quartz, corundum and zircon. With decreasing pressure the diamonds dissolve back into the rock. To occur and survive in a metastable state at the surface they must arrive from depth quickly.
Diamond may be found in kimberlite, and also occasionally in eclogite.

Alteration

Diamond is the high pressure polymorph of graphite. At 800oC diamond is the stable polymorph at pressures above about 35 kbar.

Coexistence of diamond and carbonate minerals:
The coexistence of diamond and carbonate minerals in mantle eclogite is explained by the reaction:
dolomite + coesitediopside + diamond + oxygen
MgCa(CO3)2 + 2SiO2 → CaMgSi2O6 + 2C + 2O2

Diaspore

Formula: AlO(OH) oxide containing hydroxyl
Specific gravity:
Hardness: 6½ to 7
Streak: White
Colour: White, brown, colourless, pale yellow, greyish, greenish grey, lilac, pinkish
Solubility: Insoluble in hydrochloric, sulphuric and nitric acids
Environments

Pegmatites
Metamorphic environments
Hydrothermal environments

Diaspore occurs most commonly in metamorphic bauxite deposits such as that in Mugla Province, Turkey, associated with gibbsite and böhmite. At this deposit, medium to high grade metamorphism changes syenite and nepheline syenite to gneiss, limestone to marble, and mudstone to schist. The diaspore occurs in hydrothermally mineralised fractures formed below 515oC in a deposit of metamorphosed bauxite in marble, associated with calcite, muscovite and chloritoid on a goethite-rich matrix. It is also found in emery schist in the Russian Urals and in marble at Campolonga, Switzerland.
Diaspore is found in nepheline syenite pegmatites at Ovre Åro, Norway.
Hydrothermal diaspore is a characteristic mineral of advanced alteration resulting from the reaction of low pH (acid) fluids with rocks. It forms at intermediate temperatures associated with pyrophyllite. Diaspore does not exist in equilibrium with quartz, but both minerals are usually present in specimens or outcrops of diaspore.
It is a mineral of the blueschist, prehnite-pumpellyite, greenschist and albite-epidote-hornfels facies.

Alteration

diaspore to corundum and H2O
2AlO(OH) ⇌ Al2O3 + H2O
The equilibrium temperature for this reaction at 1 kbar pressure is about 320oC (albite-epidote-hornfels facies), and at 10 kbar pressure it is about 490oC (greenschist facies). The equilibrium is to the right at higher temperatures, and to the left at lower temperatures.

diaspore and quartz to kyanite and H2O
2AlO(OH) + SiO2 ⇌ Al2OSiO4 + H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 420oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

diaspore and quartz to pyrophyllite
2AlO(OH) + 4SiO2 ⇌ Al2Si4O10(OH)2
The equilibrium temperature for this reaction at 5 kbar pressure is about 160oC (zeolite facies), and at 10 kbar it is about 300oC (blueschist facies). The equilibrium is to the right at higher temperatures, and to the left at lower temperatures.

kaolinite to diaspore, SiO2 and H2O
Al2Si2O5(OH)4 ⇌ 2AlO(OH) + 2SiO2 (aqueous) + H2O
At 10 kbar pressure the equilibrium temperature is about 300oC (blueschist facies).
At 1 kbar pressure kaolinite is stable at temperatures less than 300oC; it can be in equilibrium with quartz and water in solutions both saturated and undersaturated with quartz. Diaspore is stable at temperatures less than 400oC but only in solutions undersaturated with quartz. High temperature and low quartz saturation favours the forward reaction.

kaolinite to pyrophyllite, diaspore and H2O
2Al2Si2O5(OH)4 → Al2Si4O10(OH)2 + 2AlO(OH) + 2H2O
In the absence of quartz, kaolinite breaks down on heating according to the above reaction.
At 5 kbar pressure the equilibrium temperature for the reaction is about 320oC (prehnite-pumpellyite facies), and at 9 kbar it is about 380oC (greenschist facies).

kaolinite and diaspore to andalusite and H2O
Al2Si2O5(OH)4 + 2AlO(OH) ⇌ 2Al2OSiO4 + 3H2O
At 1 kbar pressure the equilibrium temperature for the reaction is about 320oC (albite-epidote-hornfels facies), with the equilibrium to the right at higher temperatures and to the left at lower temperatures.

kaolinite and diaspore to kyanite and H2O
Al2Si2O5(OH)4 + 2AlO(OH) ⇌ 2Al2OSiO4 + 3H2O
At 5 kbar pressure the equilibrium temperature for the reaction is about 370oC (greenschist facies), with the equilibrium to the right at higher temperatures and to the left at lower temperatures.

lawsonite and diaspore to margarite and H2O
CaAl2(Si2O7)(OH)2.H2O + 2AlO(OH) ⇌ CaAl2(Al2Si2O10)(OH)2 + 2H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 460oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

pyrophyllite and diaspore to andalusite and H2O
Al2Si4O10(OH)2 + 6AlO(OH) ⇌ 4Al2SiO5 + 4H2O
This reacton is a low pressure reaction, occurring below about 1.9 kbar. Increasing temperature favours the forward reaction.

pyrophyllite and diaspore to kyanite and H2O
Al2Si4O10(OH)2 + 6AlO(OH) ⇌ 4Al2OSiO4 + 4H2O
This reacton is a higher pressure reaction, occurring above about 1.9 kbar. Increasing temperature favours the forward reaction. At 9 kbar pressure the equilibrium temperature is about 380oC (greenschist facies).

zoisite, kyanite and diaspore to margarite
Ca2Al3[Si2O7][SiO4]O(OH) + Al2OSiO4 + 3AlO(OH) ⇌ 2CaAl2(Al2Si2O10)(OH)2
The equilibrium temperature for this reaction at 12 kbar pressure is about 480oC (blueschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

Common impurities: Fe,Mn,Cr,Si

Diopside

Formula: CaMgSi2O6 inosilicate (chain silicate), one of the most common members of the pyroxene group.
Specific gravity: 3.22 to 3.38
Hardness: 5½ to 6½
Streak: White
Colour: Green, brown, colourless
Melting point: About 1,400oC at atmospheric pressure
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments:

Plutonic igneous environments
Carbonatites
Metamorphic environments

Diopside is a common metamorphic mineral formed by the metamorphism of siliceous, magnesium-rich limestone or dolostone. It may be found in granite, skarn, marble, eclogite and kimberlite.
It often occurs in marble associated with spinel, phlogopite, tremolite and grossular.
In hornfels of contact and regional metamorphic rocks diopside is found in association with phlogopite, chondrodite and actinolite.
In carbonatites it occurs in association with dolomite, fluorite and andradite.
Other associations include tremolite, scapolite, vesuvianite, garnet and titanite. It is a mineral of the hornblende-hornfels, pyroxene-hornfels, greenschist, amphibolite and granulite facies.
At the Pyrites Mica mine, St Lawrence county, New York, USA, diopside often forms a matrix for larger meonite crystals, and sometimes has associated titanite and pyrite.

Alteration

During the progressive metamorphism of silica-rich dolostones the following approximate sequence of mineral formation is often found, beginning with the lowest temperature product: talc, tremolite, diopside, forsterite, wollastonite, periclase, monticellite

calcite
Ca2MgSi2O7 + CO2 ⇌ CaMgSi2O6 + CaCO3
The maximum stability limit of åkermanite in the presence of excess CO2 is about 6 kbar. Below that pressure, at relatively lower temperatures, åkermanite reacts with CO2 to form diopside and calcite according to the above reaction.

albite, diopside and magnetite to aegirine, Si2O6, garnet and quartz
2Na(AlSi3O8) + CaMgSi2O6 + Fe2+Fe3+2O4 ⇌ 2NaFe3+Si2O6 + Si2O6 + CaMgFe2+Al2(SiO4)3 + SiO2
This reaction may occur in blueschist facies rocks in Japan.

calcium amphibole, calcite and quartz to diopside-hedenbergite, anorthite, CO2 and H2O
Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + 3CaCO3 + 4SiO2 = 3Ca(Fe,Mg)Si2O6 + 2Ca(Al2Si2O8) + 3CO2 + H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

calcium amphibole, grossular and quartz to diopside- hedenbergite, anorthite, pyrope-almandine and H2O
2Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + Ca3Al2(SiO4)3 + SiO2 = 3Ca(Fe,Mg)Si2O6 + 4Ca(Al2Si2O8) + (Mg,Fe2+)3Al2(SiO4)3 + 2H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

ankerite-dolomite and quartz to diopside-hedenbergite and CO2
Ca(Fe,Mg)(CO3)2 + 2SiO2 = Ca(Fe,Mg)Si2O6 + 2CO2

antigorite and calcite to forsterite, diopside, CO2 and H2O
3Mg3Si2O5(OH)4 + CaCO3 → 4Mg2SiO4 + CaMgSi2O6 + CO2 +6 H2O
This reaction has been found to occur in antigorite schist at about 3 kbar pressure and 400 to 500oC (greenschist facies).

Fe-rich cordierite and diopside-hedenbergite to enstatite- ferrosilite, anorthite and quartz
(Mg,Fe)2 Al4Si5O18 + 2Ca(Mg,Fe)Si2O6 = 4(Mg,Fe2+)SiO3 + 2Ca(Al2Si2O8) + SiO2

diopside, CO2 and H2O to tremolite, calcite and quartz
5CaMgSi2O6 + 3CO2 + H2O = Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 2SiO2
Diopside is produced by the metamorphism of siliceous dolostone, and if water is introduced at a later stage tremolite may be produced from the above reaction, or by the reaction of diopside with dolomite.

diopside and albite to omphacite and quartz
CaMgSi2O6 + xNaAlSi3O8 ⇌ CaMgSi2O6.xNaAlSi2O6 + SiO2

diopside and antigorite to forsterite, Mg-rich tremolite and H2O
2CaMgSi2O6 + 5Mg3Si2O5(OH)4 ⇌ 6Mg2SIO4 + Ca2Mg5Si8O22(OH)2 + 9H2O
At 10 kbar pressure the equilibrium temperature is about 580oC (amphibolite facies).

diopside and dolomite to forsterite, calcite and CO2
CaMgSi2O6 + 3CaMg(CO3)2 → 2Mg2SiO4 + 4CaCO3 + 2CO2
This is a high-grade metamorphic change occurring at temperature in excess of 600oC.

diopside, dolomite, CO2 and H2O to tremolite and calcite
4CaMgSi2O6 + CaMg(CO3)2 + CO2 + H2O = Ca2Mg5Si8O22(OH)2 + 3CaCO3
2 and H2O.

diopside, dolomite and H2O ⇌ hydroxylclinohumite, calcite and CO2
2CaMgSi2O6 + 7CaMg(CO3)2 + H2O ⇌ 4Mg2SiO4.Mg(OH)2 + 9CaCO3 + 5CO2
In the nodular dolomites, clinohumite associated with calcite occurs in a narrow zone in the central parts of the nodules due to the above reaction

diopside, forsterite and calcite to monticellite and CO2
CaMgSi2O6 + Mg2SiO4 + 2CaCO3 → 3CaMgSiO4 + 2CO2
This reaction requires a high temperature.

diopside-hedenbergite and CO2 to enstatite-ferrosilite, calcite and quartz
Ca(Mg,Fe)Si2O6 + CO2 → (Mg,Fe2+)SiO3 + CaCO3 + SiO2

dolomite and coesite to diopside and diamond and oxygen
MgCa(CO3)2 + 2SiO2 → CaMgSi2O6 + 2C + 2O2
The coexistence of diamond and carbonate minerals in mantle eclogite is explained by the above reaction.

dolomite and quartz to diopside and CO2
CaMg(CO3)2 + 2SiO2 → CaMgSi2O6 + 2CO2
In the metamorphism of siliceous dolostone dolomite and quartz may react to form either diopside or forsterite, with diopside forming at a lower temperature than forsterite.

dolomite, tremolite and forsterite to diopside, enstatite and H2O
Ca2Mg5Si8O22(OH)2 + Mg2SiO4 ⇌ 2CaMgSi2O6 + H2O
At a pressure of 4 kbar the equilibrium temperature is about 840oC (granulite facies).

enstatite and calcite to forsterite, diopside and CO2
3Mg2Si2O6 + 2CaCO3 ⇌ 2Mg2SiO4 + 2CaMgSi2O6 + 2CO2
Enstatite is uncommon in the more calcareous hornfels due to reactions such as the above.

enstatite, calcite and quartz to diopside and CO2
3Mg2Si2O6 + 2CaCO3 + 2SiO2 ⇌ + 2CaMgSi2O6 + 2CO2
Enstatite is uncommon in the more calcareous hornfels due to reactions such as the above.

Al-rich enstatite and Al-rich diopside to forsterite, enstatite, diopside and anorthite
Mg9Al2Si9O30 + Ca5Mg4Al2Si9O30 ⇌ 2Mg2SiO4 + 3Mg2Si2O6 + 3CaMgSi2O6 + 2Ca(Al2Si2O8)
This reaction occurs at fairly low temperature and pressure.


enstatite-ferrosilite, diopside-hedenbergite, albite, anorthite and H2O to amphibole and quartz
3(Mg,Fe2+)SiO3 + Ca(Mg,Fe2+)Si2O6 + NaAlSi3O8 + Ca(Al2Si2O8) + H2O ⇌ NaCa2(Mg,Fe)4Al(Al2O6)O22(OH)2 + 4SiO2 This reaction represents metamorphic reactions between the granulite and amphibolite facies.

enstatite-ferrosilite, Fe-rich diopside and Fe, Cr-rich spinel to garnet and olivine
2(Mg,Fe2+)SiO3 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4

forsterite and åkermanite to diopside and monticellite
Mg2SiO4 + 2Ca2MgSi2O7 → CaMgSi2O6 + 3CaMg(SiO4)

forsterite and anorthite to clinoenstatite, diopside and spinel
2Mg2SiO4 + CaAl2Si2O8 ⇌ 2MgSiO3 + CaMgSi2O6 + MgAl2O4
The reaction can proceed in either direction, depending on the ambient conditions.

forsterite and anorthite to enstatite, diopside and spinel
2Mg2SiO4 + Ca(Al2Si2O8)= Mg2Si2O6 + CaMgSi2O6 + MgAl2O4

forsterite, calcite and SiO2 to diopside and CO2
Mg2SiO4 + 2CaCO3 + 3SiO2 → 2CaMgSi2O6 + 2CO2
In high temperature environments with excess SiO2 diopside may form accoring to the above reaction.

forsterite, diopside and calcite to monticellite and CO2
Mg2SiO4 + CaMgSi2O6 + 2 CaCO3 = 3CaMg(SiO4) + 2CO2

forsterite, diopside and calcite to monticellite and CO2
Mg2SiO4 + CaMgSi2O6 + 2 CaCO3 ⇌ 3CaMg(SiO4) + 2 CO2
This reaction occurs during contact metamorphism of magnesian limestone.

grossular, diopside,monticellite, calcite and H2O to vesuvianite, quartz and CO2
10Ca3Al2(SiO4)3 + 3CaMgSi2O6 + 3CaMg(SiO4) + 2CaCO3 + 8H2O ⇌ 2Ca19Al10Mg3(SiO4)10 (Si2O2)4O2(OH)8 + 3SiO2 + 2CO2
A common association in calc-silicate metamorphism can be represented by the above equation. Vesuvianite stability will tend to increase with increasing water and decrease as the activity of CO2 rises.

hornblende, calcite and quartz to Fe-rich diopside, anorthite, CO2 and H2O
Ca2(Mg,Fe2+)3(Al4Si6)O22(OH)2 + 3CaCO3 + 4SiO2 = 3Ca(Mg,Fe2+)Si2O6 + 2Ca(Al2Si2O8) + 3CO2 + H2O
Fe-rich diopside occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies. The above reaction is typical.

hornblende, grossular and quartz to Fe-rich diopside, anorthite, almandine and H2O
2Ca2(Mg,Fe2+)3(Al4Si6)O22(OH)2 + Ca3Al2Si3O12 + 2SiO2 = 3Ca(Mg,Fe2+)Si2O6 + 4CaAl2Si2O8 + (Mg,Fe2+)Al2Si3O12 + 2H2O
Fe-rich diopside occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies. The above reaction is typical. jadeite, diopside, magnetite and quartz to aegirine, kushiroite (pyroxene) and hypersthene
2NaAlSi2O6 + CaMgSi2O6 + Fe2+Fe3+2O4 + SiO2 ⇌ 2NaFe3+Si2O6 + CaAlAlSiO6 + MgFeSi2O6
Aegirine in blueschist facies rocks may be formed by the above reaction.

labradorite, albite, forsterite and diopside to omphacite, garnet and quartz
3CaAl2Si2O8 + 2Na(AlSi3O8) + 3Mg2SiO4 + nCaMgSi2O6 → (2NaAlSi2O6 + nCaMgSi2O6) + 3(CaMg2)Al2(SiO4)3 + 2SiO2
This reaction occurs at high temperature and pressure.

monticellite and diopside to åkermanite and forsterite
3CaMgSiO4 + CaMgSi2O6 ⇌ 2Ca2MgSi27 + Mg2O7
Monticellite is stable below 890oC at pressure of about 4.3 kbar (granulite facies).

nepheline and diopside to melilite, forsterite and albite
3NaAlSiO4 + 8CaMgSi2O6 ⇌ 4Ca2MgSi2O7 + 2Mg2SiO4 + 3NaAlSi3O8
This reaction is in equilibrium at about 1180oC, with lower temperatures favouring the forward reaction.

phlogopite, calcite and quartz to diopside, microcline, H2O and CO2
KMg3(AlSi3O10)(OH)2 + 3CaCO3 + 6SiO2 = 3CaMgSi2O6 + K(AlSi3O8) + H2O + 3CO2
In reaction zones between interbedded carbonate and pelitic beds of the calc-mica schists, phlogopite may alter according to the above reaction.

orthopyroxene, Fe-rich diopside and Fe and Cr-rich spinel to Fe, Ca and Cr-rich pyrope and olivine
(Mg,Fe)2Si2O6 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ (Mg,Fe)2Ca(Al,Cr)2Si3O12 + (Mg,Fe)2Ca(Al,Cr)2Si3O12 + (Fe,Mg)2SiO4
The garnet-bearing peridotites are considered to have originated in a high-pressure environment according to the reaction

serpentine and diopside to tremolite, forsterite and H2O
5Mg3Si2O5(OH)4 + 2CaMgSi2O6 ⇌ Ca2Mg5Si8O22(OH)2 + 6Mg2SiO4 + 9H2O + H2O
In lower grade assemblages associated with contact and regional metamorphism serpentine may form tremolite and forsterite according to the above reaction.

Fe and Cr-rich spinel , diopside and enstatite to forsterite, anorthite and chromite
MgFeAl2Cr2O8 + CaMgSi2O6 + Mg2Si2O6 ⇌ 2Mg2SiO4 + Ca(Al2Si2O8) + Fe2+Cr2O4 This reaction occurs at fairly low temperature and pressure.

tremolite to diopside, enstatite and quartz
Ca2Mg5Si8O22(OH)2 ⇌ 2CaMgSi2O6 + 3MgSiO3 + SiO2 + H2O
The equilibrium temperature for this reaction at 8 kbar pressure is 930oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures (for the same pressure).

tremolite and calcite to diopside, dolomite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 3CaCO3 ⇌ 4CaMgSi2O6 + CaMg(CO3)2 + CO2 + H2O
The forward reaction is a diopside-forming metamorphic reaction.

tremolite, calcite and quartz to diopside, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 2SiO2 → 5CaMgSi2O6 + 3CO2 + H2O
This is a medium-grade metamorphic change occurring at temperature between about 450oC and 600oC.

tremolite and forsterite to diopside, enstatite and H2O
Ca2Mg5Si8O22(OH)2 + Mg2SiO4 ⇌ 2CaMgSi2O6 + H2O
The equilibrium temperature for this reaction at 4 kbar pressure is 840oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

Common impurities: Fe,V,Cr,Mn,Zn,Al,Ti,Na,K

Dioptase

Formula: CuSiO3.H2O cyclosilicate (ring silicate)
Specific gravity: 3.3
Hardness: 5
Streak: Green
Colour: Emerald green
Solubility: Moderately soluble in hydrochloric acid
Environments:

Hydrothermal environments

Dioptase occurs in the oxidation zone of high temperature hydrothermal deposits.

Dolomite

Formula: CaMg(CO3)2 carbonate
Specific gravity: 2.84 to 2.86
Hardness: 3½ to 4
Streak: White
Colour: Colourless, white, gray, reddish-white, brownish-white, or pink; colourless in transmitted light
Solubility: Readily soluble in hydrochloric acid
Environments:

Carbonatites (essential)
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Dolomite overwhelmingly occurs in dolostone or in marble formed from the contact metamorphism of dolostone. It is a mineral of the prehnite-pumpellyite, greenschist, amphibolite facies and granulite facies. It also occurs in hypothermal (high temperature), mesothermal (moderate temperature) and epithermal (low temperature) veins, chiefly in lead and zinc veins in limestone, associated with quartz, fluorite, calcite, baryte, magnesite, sphalerite, siderite, galena, pyrite and chalcopyrite.
Few dolomites are primary in origin. The main exception to this is primary dolomite that forms in evaporites as a relatively late product of seawater evaporation. These primary dolomites, however, are rare.
Sedimentary dolomite results from alteration of calcite and aragonite. In sedimentary dolostone, dolomite is often associated with calcite, aragonite, gypsum, anhydrite and halite.
Although uncommon, when dolomite occurs in altered ultramafic igneous rocks, such as serpentinite, it may be associated with magnesite, serpentine and talc.
Dolomite is an essential constituent of dolostone.
It is a common but not esential constituent of limestone and skarn.
It also may be found in marble and serpentinite.
It is a mineral of the prehnite-pumpellyite, greenschist, amphibolite and granulite facies.

Alteration

ankerite, dolomite and quartz to augite and CO2
Ca(Mg,Fe)(CO3)2 + 2SiO2 → Ca(Mg,Fe)Si2O6 + 2CO2

ankerite-dolomite and quartz to diopside-hedenbergite and CO2
Ca(Fe,Mg)(CO3)2 + 2SiO2 = Ca(Fe,Mg)Si2O6 + 2CO2

aragonite or calcite and Mg2+ (from Mg-rich fluid) to dolomite and Ca2+
2CaCO3 + Mg2+ ⇌ CaMg(CO3)2 + Ca2+

diopside and dolomite to forsterite, calcite and CO2
CaMgSi2O6 + 3CaMg(CO3)2 → 2Mg2SiO4 + 4CaCO3 + 2CO2
This is a high-grade metamorphic change occurring at temperature in excess of 600oC.

diopside, dolomite, CO2 and H2O to tremolite and calcite
4CaMgSi2O6 + CaMg(CO3)2 + CO2 + H2O = Ca2Mg5Si8O22(OH)2 + 3CaCO3
Diopside is produced by the metamorphism of siliceous dolostone, and if water is introduced at a later stage tremolite may be produced from the above reaction, or by the reaction of diopside with CO2 and H2O.

diopside, dolomite and H2O ⇌ hydroxylclinohumite, calcite and CO2
2CaMgSi2O6 + 7CaMg(CO3)2 + H2O ⇌ 4Mg2SiO4.Mg(OH)2 + 9CaCO3 + 5CO2
In the nodular dolomites, clinohumite associated with calcite occurs in a narrow zone in the central parts of the nodules due to the above reaction

dolomite and chert to talc and calcite
3CaMg(CO3)2 + 4SiO2 + H2O → Mg3Si4O10(OH)2 + 3CaCO3 + 3CO2
Metamorphism of siliceous carbonate rocks causes the formation of hydrous phases such as talc and tremolite. This is a very low-grade metamorphic reaction occurring at temperature between about 150oC and 250oC.

dolomite and coesite to diopside, diamond and oxygen
MgCa(CO3)2 + 2SiO2 → CaMgSi2O6 + 2C + 2O2
The coexistence of diamond and carbonate minerals in mantle eclogite is explained by the above reaction.

dolomite, K-feldspar and H2O to phlogopite, calcite and CO2
3CaMg(CO3)2 + KAlSi3O8 + H2O = KMg3AlSi3O10(OH)2 + 3CaCO3 + 3CO2
In the presence of Al and K the metamorphism of dolomite leads to the formation of phlogopite according to the above equation.

dolomite and quartz to diopside and CO2
CaMg(CO3)2 + 2SiO2 → CaMgSi2O6 + 2CO2
In siliceous dolostone dolomite and quartz may react to form either diopside or forsterite, with diopside forming at a lower temperature than forsterite.

dolomite and quartz to forsterite, calcite and CO2
2CaMg(CO3)2 + SiO2 → Mg2SiO4 + 2CaCO3 + 2CO2 In siliceous dolostone dolomite and quartz may react to form either diopside or forsterite, with diopside forming at a lower temperature than forsterite.

dolomite and quartz to diopside and CO2
CaMg(CO3)2 + 2SiO2 → CaMgSi2O6 + 2CO2
This reaction is the result of metamorphism of siliceous, Mg-rich limestones or dolostones. dolomite, quartz and H2O to tremolite, calcite and CO2
5CaMg(CO3)2 + 8SiO2 + H2O → Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 7CO2
This is a metamorphic reaction in dolomitic limestone

dolomite and tremolite to forsterite, calcite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 11CaMg(CO3)2 → 8Mg2SiO4 + 13CaCO3 + 9CO2 + H2O

dolomite, tremolite and forsterite to diopside, enstatite and H2O
Ca2Mg5Si8O22(OH)2 + Mg2SiO4 ⇌ 2CaMgSi2O6 + H2O
At a pressure of 4 kbar the equilibrium temperature is about 840oC (granulite facies).

forsterite, dolomite and H2O to calcite, hydroxylclinohumite and CO2
A forsterite-clinohumite assemblage in the silica-rich dolomite in the aureole of the Alta granodiorite in Utah, USA, is probably due to the reaction:
4Mg2SiO4 + CaMg(CO3)2 + H2O → Mg9(SiO4)4(OH)2 +CaCO3 + CO2
A forsterite-clinohumite assemblage in the silica-rich dolomite in the aureole of the Alta granodiorite in Utah, USA, is probably due to the above reaction.

kaolinite, dolomite, quartz and H2O to chlorite, calcite and CO2
Al2Si2O5(OH)4 + 5CaMg(CO3)2 + SiO2 + 2H2O ⇌ Mg5Al(AlSi3O10)(OH)8 + 5CaCO3 + 5CO2
Chlorite often forms in this way from reactions between clay minerals such as kaolinite and carbonates such as dolomite.

talc, calcite and CO2 to dolomite, quartz and H2O
Mg3Si4O10(OH)2 + 3CaCO3 + 3CO2 ⇌ 3CaMg(CO3)2 + 4SiO2 + H2O

talc and calcite to tremolite dolomite, CO2 and H2O
2Mg3Si4O10(OH)2 + 3CaCO3 +4SiO2 → Ca2Mg5Si8O22(OH)2 + CaMg(CO3)2 + CO2 +H2O
This is a low-grade metamorphic change, occurring at temperature between about 250oC and 450oC.

tremolite and calcite to diopside, dolomite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 3CaCO3 ⇌ 4CaMgSi2O6 + CaMg(CO3)2 + CO2 + H2O
The forward reaction is a diopside-forming metamorphic reaction.

tremolite and dolomite to forsterite, calcite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 11CaMg(CO3)2 → 8Mg2SiO4 + 13CaCO3 + 9CO2 + H2O

tremolite, dolomite and H2O ⇆ hydroxylclinohumite, calcite and CO2
Ca2Mg5Si8O22(OH)2 + 13CaMg(CO3)2 + H2O ⇆ 2(4Mg2SiO4.Mg(OH)2) + 15CaCO3 + 11CO2

Common impurities: Fe,Mn,Co,Pb,Zn

Duftite

Formula: PbCu(AsO4)(OH) anhydrous arsenate containing hydroxyl
Adelite-Descloizite Group. Conichalcite-Duftite Series. Duftite-Mottramite Series.
Specific gravity: 6.12
Hardness: 4½
Streak: Pale green, white
Colour: Olive-green, grey-green; light apple-green in transmitted light.
Environments:

Hydrothermal environments

Duftite is a secondary mineral that occurs in the oxidised zone of hydrothermal metal ore deposits. At the type locality it is associated with azurite

Localities

United Kingdom

At Arm O'Grain, Cumbria, mottramite and duftite are almost indistinguishable, due to much arsenate substitution for vanadate in mottramite. It occurs with mimetite.

At Driggith and Sandbed Mines, Cumbria, duftite is associated with mottramite.

At Short Grain, Cumbria, duftite occurs rarely in vugs in quartz and baryte, commonly overgrown by mimetite.

USA

At the San Rafael Mine, Nevada, duftite occurs in pods of limonite associated with adamite, segnitite, wulfenite and mimetite.

Dussertite

Formula: BaFe3+3(AsO4)(AsO3OH)(OH)6
Specific gravity: 3.75
Hardness: 3½
Colour: Green, yellow-green, bluish green; yellowish green in transmitted light.
Solubility: Soluble in dilute hydrochloric acid
Dussertite is a secondary mineral, frequently an alteration product of arsenopyrite. At the type locality, Djebel Debar, Algeria, it is found as crusts on tabular or cavernous quartz.

Edenite

Formula: NaCa2Mg5(Si7Al)O22(OH)2 inosilicate (chain silicate) amphibole
Specific gravity: 3.00 to 3.06 (Webmin)
Hardness: 5 to 6
Streak: White
Colour: Green, brown, white
Environments:

Plutonic igneous environments
Metamorphic environments

Edenite occure in plutonic igneous rocks and in medium-grade metamorphic rocks such as marble.

Common impurities: Ti,Mn,K,P

Enargite

Formula: Cu3AsS4 sulphosalt
Specific gravity: 4.4
Hardness: 3½
Streak: Black
Colour: Steel grey to iron black
Solubility: Slightly soluble in nitric acid
Environments:

Hydrothermal environments

Enargite is a comparatively rare mineral, found in vein and replacement deposits formed at moderate temperatures associated with pyrite, sphalerite, bornite, galena, tetrahedrite, covellite and chalcocite. Enargite occurs in arsenic containing copper ore veins.

Common impurities: Sb,Fe,Pb,Zn,Ag,Ge

Englishite

Formula: K3Na2Ca10Al15(OH)7(PO4)21.26H2O hydrated phosphate with hydroxyl
Specific gravity: 2.68
Hardness: about 3
Streak: White
Colour: Colourless to white, grayish green, colourless in transmitted light
Environments:

Pegmatites
Hydrothermal environments

Englishite occurs in variscite nodules at the type locality Clay Canyon, Utah, USA, associated with montgomeryite, wardite, millisite and crandallite. It is also found in the Tip Top pegmatite, South Dakota, USA, associated with crandallite and other phosphates.

Enstatite

Formula: Mg2Si2O6 inosilicate (chain silicate) pyroxene group
Specific gravity: 3.2 to 3.9
Hardness: 5 to 6
Streak: Grey to white
Colour: Green, brown, white
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Volcanic igneous environments
Metamorphic environments

Enstatite is a widespread mineral of the pyroxene group. It usually occurs in magnesium- and iron-rich igneous rocks and in both iron and stony meteorites.
In igneous rocks, a high silica melt will give augite, hornblende and enstatite or biotite.
Metamorphic enstatite is a mineral of the greenschist, amphibolite, eclogite and granulite facies.

Alteration

anorthite, enstatite, spinel, K2O and H2O to Al-rich hornblende, Mg-rich sapphirine and phlogopite
2.5Ca(Al2Si2O8) + 5Mg2Si2O6 + 6MgAl2O4 + K2O + 3H2O → Ca2.5Mg4Al(Al2Si6)O22(OH)2 + 3Mg2Al4SiO10 + 2KMg3(AlSi3O10)(OH)2
This reaction occurs as the metamorphic grade decreases from the granulite to the amphibolite facies.

anthophyllite to enstatite, quartz and H2O
2☐Mg2Mg5Si8O22(OH)2 ⇌ 7Mg2Si2O6 + 2SiO2 + 2H2O
At 10 kbar pressure the equilibrium temperature is about 810oC (granulite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures.

anthophyllite and forsterite to enstatite and H2O
2☐Mg2Mg5Si8O22(OH)2 + 2Mg2SiO4 ⇌ 9Mg2Si2O6 + 2H2O
At 2 kbar pressure the equilibrium temperature is about 690oC (pyroxene-hornfels facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures.

augite and andalusite to enstatite- ferrosilite and anorthite
2Ca(Fe,Mg)Si2O6 + 2Al2SiO5 → (Mg,Fe2+)2Si2O6 + 2Ca(Al2Si2O8)

biotite and quartz to enstatite-ferrosilite, orthoclase and H2O
2K(Mg,Fe)3(AlSi3O10)(OH)2 + 6SiO2 → 3(Mg,Fe2+)2Si2O6 + 2KAlSi3O8 + 2H2O
Enstatite-ferrosilite may develop from the breakdown of biotite according to the above reaction.

chlorite and quartz to enstatite-ferrosilite, Fe-rich cordierite and H2O
(Mg,Fe2+)4Al4Si2O10(OH)8 + 5SiO2 → (Mg,Fe2+)2Si2O6 + (Mg,Fe2+2)2Al4Si5O18 + 4H2O
Enstatite-ferrosilite also occurs in medium grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content according to the above equation.

Fe-rich cordierite and diopside-hedenbergite to enstatite-ferrosilite, anorthite and quartz
(Mg,Fe)2 Al4Si5O18 + 2Ca(Mg,Fe)Si2O6 = 2(Mg,Fe2+)2Si2O6 + 2Ca(Al2Si2O8) + SiO2

corundum and forsterite to spinel and enstatite
2Al2O3 + 2Mg2SiO4 ⇌ 2MgAl2O4 + Mg2Si2O6
At 10 kbar pressure the equilibrium temperature is about 570oC (amphibolite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

cummingtonite-grunerite and olivine to enstatite-ferrosilite and H2O
2(Fe,Mg)7Si8O22(OH)2 + 2(Mg,Fe)2SiO4 ⇌ 9(Mg,Fe2+)2Si2O6 + 2H2O

diopside-hedenbergite and CO2 to enstatite-ferrosilite, calcite and quartz
2Ca(Mg,Fe)Si2O6 + 2CO2 → (Mg,Fe2+)2Si2O6 + 2CaCO3 + 2SiO2

dolomite, tremolite and forsterite to diopside, enstatite and H2O
Ca2Mg5Si8O22(OH)2 + Mg2SiO4 ⇌ 2CaMgSi2O6 + H2O
At a pressure of 4 kbar the equilibrium temperature is about 840oC (granulite facies).

enstatite and H2O to forsterite and cummingtonite
9Mg2Si2O6 + 2H2O = 2Mg2SiO4 + 2Mg2Mg5Si8O22(OH)2
Cummingtonite may be formed by retrograde metamorphism according to the above reaction.

enstatite and calcite to forsterite, diopside and CO2
3Mg2Si2O6 + 2CaCO3 ⇌ 2Mg2SiO4 + 2CaMgSi2O6 + 2CO2
Enstatite is uncommon in the more calcareous hornfels due to reactions such as the above.

enstatite, calcite and quartz to diopside and CO2
3Mg2Si2O6 + 2CaCO3 + 2SiO2 ⇌ + 2CaMgSi2O6 + 2CO2
Enstatite is uncommon in the more calcareous hornfels due to reactions such as the above.

enstatite and corundum to cordierite and spinel
5Mg2Si2O6 + 10Al2O3 ⇌ 2Mg2Al4Si5O18 + 6MgAl2O4
At 6 kbar pressure the equilibrium temperature is about 715oC (amphibolite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

enstatite and corundum to pyrope
3Mg2Si2O6 + 2Al2O3 ⇌ 2Mg3Al2(SiO4)3
At 14 kbar pressure the equilibrium temperature is about 810oC (eclogite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

Al-rich enstatite and Al-rich diopside to forsterite, enstatite, diopside and anorthite
Mg9Al2Si9O30 + Ca5Mg4Al2Si9O30 ⇌ 2Mg2SiO4 + 3Mg2Si2O6 + 3CaMgSi2O6 + 2Ca(Al2Si2O8)
This reaction occurs at fairly low temperature and pressure.

enstatite, kyanite and quartz to cordierite
Mg2Si2O6 + 2Al2OSiO4 + SiO2 ⇌ Mg2Al4Si5O18
At 6 kbar pressure the equilibrium temperature is about 475oC (greenschist facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

enstatite and spinel to forsterite and cordierite
5Mg2Si2O6 + 2MgAl2O4 ⇌ 5Mg2SiO4 + Mg2Al4Si5O18
At 4 kbar pressure the equilibrium temperature is about 715oC (amphibolite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

enstatite-ferrosilite and H2O to serpentine and quartz
3(Mg,Fe2+)2Si2O6 + 4H2O ⇌ (Fe,Mg)6Si4O10(OH)8 +2SiO2

enstatite-ferrosilite and andalusite to Fe-rich cordierite and spinel-hercynite
5(Mg,Fe2+)2Si2O6 + 10Al2SiO5 → 4(Mg,Fe2+)2Al4Si5O18 + 2(Mg,Fe2+)Al2O4
In medium-grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content, in an SiO2 deficient environment the association of andalusite with enstatite-ferrosilite is excluded by the above reaction.

enstatite-ferrosilite, andalusite and quartz to Fe-rich cordierite
(Mg,Fe2+)2Si2O6 + 2Al2SiO5 + SiO2 → (Mg,Fe2+)2Al4Si5O18
In medium-grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content, the association of andalusite with enstatite-ferrosilite is excluded by the above reaction.

enstatite-ferrosilite, Fe-rich diopside and Fe, Cr-rich spinel to garnet and olivine
(Mg,Fe2+)2Si2O6 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4

enstatite-ferrosilite, diopside-hedenbergite, albite, anorthite and H2O to amphibole and quartz
3(Mg,Fe2+)2Si2O6 + 2Ca(Mg,Fe2+)Si2O6 + 2NaAlSi3O8 + 2Ca(Al2Si2O8) + 2H2O ⇌ 2NaCa2(Mg,Fe)4Al(Al2O6)O22(OH)2 + 8SiO2 This reaction represents metamorphic reactions between the granulite and amphibolite facies.

enstatite-ferrosilite, K-feldspar and H2O to biotite and quartz
3(Mg,Fe2+)2Si2O6 + 2K(AlSi3O8) + 2H2O ⇌ 2K(Mg,Fe)3(AlSi3O10)(OH)2+ 6SiO2
The forward reaction leads to an amphibolite facies assemblage.

enstatite-ferrosilite, quartz and H2O to cummingtonite- grunerite
7(Mg,Fe2+)2Si2O6 + 2SiO2 + 2H2O ⇌ 2(Fe,Mg)7Si8O22(OH)2

forsterite and CO2 to enstatite and magnesite
2Mg2SiO4 + 2CO2 ⇌ Mg2Si2O6 + 2MgCO3

forsterite and anorthite to enstatite, diopside and spinel
2Mg2SiO4 + Ca(Al2Si2O8)= Mg2Si2O6 + CaMgSi2O6 + MgAl2O4

forsterite, enstatite and H2O to serpentine
2Mg2SiO4 + Mg2Si2O6 + 4H2O → 2Mg3Si2O5(OH)4
Serpentine is not stable in the presence of carbon dioxide, and may further react with it to form talc and magnesite.

forsterite and quartz to enstatite
Mg2SiO4 + SiO2 → Mg2Si2O6
Forsterite is not stable in the presence of free SiO2 and will react with it to form enstatite according to the above reaction.

forsterite and talc to enstatite and H2O
2Mg2SiO4 + 2Mg3Si4O10(OH)2 ⇌ 5Mg2Si2O6 + 2H2O
At 10 kbar pressure the equilibrium temperature is about 680oC (amphibolite facies), with equilibrium to the right at higher temperatures and to the left at lower temperatures (for the same pressure).

gedrite-ferro-gedrite and quartz to enstatite-ferrosilite, Fe-rich cordierite and H2O
2(Mg,Fe2+)5Al4Si6O22(OH)2 + 4Si2 → 3(Mg,Fe2+)2Si2O6 + 2(Mg,Fe2+)2Al4Si5O18 + 2H2O
In the pyroxene-hornfels facies enstatite-ferrosilite may develop from gedrite-ferro-gedrite according to the above reaction.

kyanite and enstatite to cordierite and corundum
3Al2O(SiO4) + Mg2Si2O6 ⇌ Mg2Al4Si5O18 + Al2O3
The equilibrium temperature for this reaction at 6 kbar pressure is about 520oC (amphibolite facies), with equilibrium to the right at higher temperatures, and to the left at lower temperatures.

kyanite and enstatite to quartz and pyrope
2Al2O(SiO4) + 3Mg2Si2O6 ⇌ 2SiO2 + 2Mg3Al2(SiO4)3
The equilibrium temperature for this reaction at 14 kbar pressure is about 950oC (granulite facies), with equilibrium to the right at higher temperatures, and to the left at lower temperatures.

olivine and CO2 to enstatite-ferrosilite and magnesite-siderite
(Mg,Fe)2SiO4 + CO2 → (Mg,Fe2+)SiO3 + (Mg,Fe)CO3

olivine and quartz to enstatite-ferrosilite
(Mg,Fe)2SiO4 + SiO2 → (Mg,Fe2+)2Si2O6

Fe and Cr-rich spinel , diopside and enstatite to forsterite, anorthite and chromite
MgFeAl2Cr2O8 + CaMgSi2O6 + Mg2Si2O6 ⇌ 2Mg2SiO4 + Ca(Al2Si2O8) + Fe2+Cr2O4
This reaction occurs at fairly low temperature and pressure.

talc to enstatite, quartz and H2O
2Mg3Si4O10(OH)2 ⇌ 3Mg2Si2O6 + 2SiO2 + 2H2O
At 10 kbar pressure the equilibrium temperature is about 790oC (granulite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures.

talc and enstatite to anthophyllite
Mg3Si4O10(OH)2 + 2Mg2Si2O6 → ☐Mg2Mg5Si8O22(OH)2
At 10 kbar pressure the equilibrium temperature is 750oC (granulite facies).

tremolite to diopside, enstatite, quartz and H2O
2Ca2Mg5Si8O22(OH)2 ⇌ 4CaMgSi2O6 + 3Mg2Si2O6 + 2SiO2 + 2H2O
The equilibrium temperature for this reaction at 8 kbar pressure is 930oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures (for the same pressure).

tremolite and forsterite to diopside, enstatite and H2O
Ca2Mg5Si8O22(OH)2 + Mg2SiO4 ⇌ 2CaMgSi2O6 + H2O
The equilibrium temperature for this reaction at 4 kbar pressure is 840oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

Common impurities: Fe,Ca,Al,Co,Ni,Mn,Ti,Cr,Na,K

Epidote

Formula: Ca2(Al2Fe3+)[Si2O7] [SiO4]O(OH) sorosilicate (Si2O7 groups) epidote group
Specific gravity: 3.38 to 3.49
Hardness: 6
Streak: White
Colour: Yellowish-green, green, brownish-green, black
Solubility: Slightly soluble in hydrochloric acid; insoluble in sulphuric and nitric acid
Environments:

Pegmatites
Metamorphic environments (typical)
Basaltic cavities

Epidote is a widespread mineral, found in veins and joint fillings in some granitic rocks, in pegmatites, and in contact and regional metamorphic environments. It is a low temperature mineral formed by metamorphism of limestone with calcium-rich garnet, diopside, vesuvianite and calcite.
Epidote may be found in gneiss and hornfels.
It is characteristic of the albite-epidote-hornfels facies and it is also a mineral of the prehnite-pumpellyite, greenschist, amphibolite and blueschist facies.

Alteration

Epidote forms as a reaction product of plagioclase feldspar, pyroxene and amphibole.

aegirine, epidote and CO2 to albite, hematite, quartz, calcite and H2O
4NaFe3+Si2O6 + 2Ca2(Al2Fe3+ [Si2O7](SiO4)O(OH) + 4CO2 → 4Na(AlSi3O8) + 3Fe2O3 + 2SiO2 + 4CaCO3 + H2O

Ca-Fe amphibole, anorthite and H2O to chlorite, epidote and quartz
CaFe5Al2Si7O22(OH)2 + 3CaAl2Si2O8 + 4H2O → Fe5Al2Si3O10(OH)8 + 2Ca2Al3Si3O12(OH) + 4SiO2

epidote and chlorite to hornblende and anorthite
6Ca2Al3(SiO4)3(OH) + Mg5Al2Si3O18(OH)8 → Ca2Mg5Si8O22(OH)2 + 10CaAl2Si2O8
This reaction represents changes when the metamorphic grade increases from the greenschist facies to the amphibolite facies.

epidote and quartz to anorthite, grossular and H2O
4Ca2Al3(SiO4)3(OH) + SiO2 → 5CaAl2Si2O8 + Ca3Al2(SiO4)3 + 2H2O
This reaction occurs as the degree of metamorphism increases

Common impurities: Al,Mg,Mn

Epistilbite

Formula: Ca3[Si18Al6O48].16H2O tectosilicate (framework silicate), zeolite group
Specific gravity: 2.22 to 2.28
Hardness: 4 to 4½
Streak: White
Colour: Colourless, white, orange, red

Environments:

Metamorphic environments
Basaltic cavities

Epistilbite occurs in cavities in silica-rich basalt and olivine basalt, associated with laumontite, heulandite and mordenite. It also occurs in gneiss. No diagenetic epistilbite has been reported.
In Iceland epistilbite occurs in geothermal wells in basalt at 80 to 160oC.

Common impurities: Fe,Mg,Na,K

Epsomite

Formula: Mg(SO4.7H2O sulphate
Specific gravity: 1.68
Hardness: 2 to 2½
Streak: White
Colour: White, sometimes greenish, reddish, yellowish
Solubility: Effloresces in dry air. Very soluble in water.
Environments:

Hot spring deposits
Hydrothermal environments

Epsomite occurs as an efflorescence on the rocks in mine workings and on the walls of caves. It occurs as deposits in salt springs and ore bodies, deposits in salt lakes and in arid regions in blueschist facies rocks.

Common impurities: Ni,Fe,Co,Mn,Zn

Erionite

The erionites are:
Erionite-Ca, Ca5[Si26Al10O72].30H2O
Erionite-K, K10[Si26Al10O72].30H2O
Erionite-Na, Na10[Si26Al10O72].30H2O
They are all tectosilicates (framework silicates) and members of the zeolite group.
Specific gravity: 2.09 to 2.13
Hardness: 3½ to 4
Streak: White
Colour: Colourless, white, green, grey, orange
Environments:

Volcanic igneous environments
Sedimentary environments
Basaltic cavities

Erionite is common in altered silicic tuff, especially in saline lake deposits, where it crystallises when the pH reaches about 8.5 (moderately alkaline). In this environment trivalent iron may substitute for aluminium in the structure.
Hydrothermal erionite occurs in cavities in volcanic rocks. It is often intergrown with offretite.
Epitaxial overgrowths of erionite on lévyne have been reported .

Localities

Austria

At Pauliberg, Burgenland, erionite needles are found on primary magnetite and hematite in vesicular basalt.

In the basalt at Kollnitz, Carinthia, erionite is found on celadonite associated with pyrite, calcite and phillipsite.

Canada

At Chase Creek, British Columbia, pure erionite without any offretite intergrowth occurs in vesicular basalt, rarely covered by paulingite, harmotome, heulandite and clay.

At Pass Valley, British Columbia, erionite intergrown with clay and associated with clinoptilolite occurs in vesicles in rhyolite.

At Twig Creek, British Columbia, erionite crystals capped by offretite line vesicles in basalt.

Denmark

Erionite covered with chabazite occurs in basalt in the Faroe Islands.

France

Near Araules, Auvergne-Rhône-Alpes, offretite intergrown with small amounts of erionite is found in basalt, associated with phillipsite, chabazite and calcite.

At Mont Semiol, Auvergne-Rhône-Alpes, erionite is found as terminations on offretite crystals in olivine basalt, associateed with mazzite, phillipsite, chabazite, calcite and siderite.

Georgia

At Shurdo, Georgia, erionite occurs in volcanic rock associated with heulandite, chabazite, mordenite, stilbite and opal.

Germany

At Sasbach, Baden-Württemberg, offretite-erionite occurs in vesicles in nepheline-olivine- augite basalt, associated with faujasite and phillipsite.

At Teichelberg, Bavaria, offretite-erionite occurs in cavities in basalt associated with gismondine, phillipsite, calcite and chabazite.

At Wiesau, Bavaria, erionite-offretite occurs in basalt with thomsonite and montmorillonite.

At the Zeilberg Quarry, Bavaria, erionite is found in basalt with dachiardite, clinoptilolite, phillipsite, natrolite, heulandite, thomsonite, laumontite, scolecite, stilbite, gmelinite, chabazite, gismondine, apophyllite, calcite, gyrolite, okenite, garronite and tobermorite.

Near Gedern, Hessen, erionite is found in the extremities of offretite needles in vesicular basalt, associated with phillipsite, chabazite, montmorillonite and, rarely, gismondine.

At Geilhausen, Hessen, offretite covered by erionite occurs in vesicles in olivine basalt, associated with chabazite and phillipsite.

At Hungen, Hessen, erionite-offretite occurs with chabazite, faujasite, ferrierite, lévyne, phillipsite and thomsonite.

At the Ortenberg Quarry, Hessen, erionite is found, rarely, in vesicles in a sandstone xenolith embedded in olivine basalt, with paulingite, clinoptilolite, nontronite, phillipsite, calcite, dachiardite, merlinoite, apophyllite and chabazite.

Italy

At Nuoro, Sardinia, erionite is found as overgrowths on lévyne.

Japan

Erionite on lévyne crystals is found in vesicular basalts at Chojabaru, Nagasaki Prefecture, associated with chabazite and stilbite.

At Narushima, Nagasaki Prefecture, erionite occurs with heulandite in the glassy margins of a rhyolite dyke.

Along the seashore of Maze, Niigata Prefecture, erionite is found associated with chabazite.

New Zealand

At Waitakere, North Island, erionite is found surrounded by lévyne.

At Moeraki, South Island, erionite occurs in altered vesicular basalt associated with chabazite, heulandite and phillipsite.

Russia

In lavas along the Nidym River, Siberia, erionite is associated with heulandite.

Tanzania

At Lake Natron, Arusha Region, eriorite is associated with phillipsite, mordenite, analcime and chabazite.

In the Olduvai Gorge, Arusha Region, erionite is abundant in sedimentary beds associated with phillipsite, clinoptilolite, chabazite and analcime.

United Kingdom

At Giant's Causeway, County Antrim, Northern Ireland, erionite occurs in basalt associated with heulandite and phillipsite.

Erionite is often intergrown with offretite on lévyne at many localities in County Antrim, Northern Ireland.

At the Storr, Isle of Skye, Scotland, erionite occurs in vesicles in basalt with massive garronite.

United States

Near Ajo, Arizona, erionite occurs in vesicular basalt associated with phillipsite, heulandite and calcite on the primary minerals hematite, augite, kaolinite, enstatite, pseudobrookite and rancieite.

At Malpais Hill, Arizona, in vesicular olivine basalt, small vugs are lined with celadonite and montmorillonite covered with offretite intergrown with erionite.

At Thum Butte, Arizona, erionite occurs in vesicular olivine basalt associated with quartz, mordenite, clinoptilolite, phillipsite and opal.

Near Freedom, Idaho, erionite occurs in vesicular basalt with chalcedony and opal.

At Reese River, Nevada, erionite occurs in lacustrine (deposited in a lake) mudstone associated with clinoptilolite, chabazite and phillipsite.

Near Aneroid Lake, Oregon, erionite occurs in vesicular basalt, frequently covered with heulandite.

Along the Beaver Divide, Wyoming, erionite and clinoptilolite occur in altered tuff.

At the Durkee fire-opal mine, Oregon, some erionite fibres are found covered by common opal and, rarely, fire opal.

At Yaquina Head, Oregon, erionite occurs in vesicular basalt associated with clinoptilolite, mordenite, phillipsite, pyrite and, rarely, dachiardite and baryte.

Erythrite

Formula: Co3(AsO4)2.8H2O arsenate, vivianite group
Specific gravity: 3.07
Hardness: 2
Streak: Pink
Colour: Red
Solubility: Insoluble in water, nitric and sulphuric acid; soluble in hydrochloric acid
Environments:

Hydrothermal environments

Erythrite is a rare secondary mineral that occurs in the oxidation zone of some Ni-Co-As mineral deposits as an alteration product of cobalt arsenides. It is rarely present in large amounts and usually forms as crusts or fine aggregates filling cracks.

Common impurities: Ni,Fe,Zn

Ettringite

Formula: Ca6Al2(SO4)3(OH)12.26H2O hydrated sulphate containing hydroxyl
Specific gravity: 1.77
Hardness: 2 to 2½
Streak: White
Colour: Colourless to white, yellow to light brown, colourless in transmitted light
Solubility: Partially decomposed by water, giving an alkaline solution. Easily soluble in dilute acids.
Environments:

Volcanic igneous environments
Metamorphic environments

Localities

Germany

Near ettringen, Rhine, ettringite occurs in cavities in metamorphosed limestone inclusions in basaltic rocks rich in leucite and nepheline.

USA

At the Lucky Cuss Mine, Arizona, ettringite is an alteration product of calcium-aluminium silicates.

At Franklin, New Jersey, ettringite occurs with andradite and manganese-rich biotite.

Eucryptite

Formula: LiAlSiO4 inosilicate, phenakite group
Specific gravity: 2.657 to 2.666
Hardness: 6½
Streak: white
Colour: Colourless, white, pale tan, pale grey
Solubility: gelatinises in acids
Environments:

Pegmatites

Eucryptite occurs in lithium-rich pegmatites, often as graphic intergrowths with albite derived from alteration of spodumene

Alteration

Eucryptite is a secondary mineral derived from spodumene and associated with albite, spodumene, petalite, amblygonite, lepidolite and quartz.
The co-occurrence of the lithium aluminium silicates spodumene LiAlSi2O6, petalite LiAlSi4O10 and eucryptite LiAlSiO4 is not common, but it does occur in some pegmatites in northern Portugal. The spodumene precipitates early from the magma, petalite later, and eucryptite is hydrothermal and secondary. On alteration spodumene is mainly replaced by albite and muscovite, and petalite by K-feldspar and eucryptite.

spodumene and Na+ to eucryptite, albite and Li+
2LiAlSi2O6 + Na+ → LiAlSiO4 + NaAlSi3O8 + Li+

Common impurities: Na,K

Evansite

Formula: Al3(PO4)(OH)6.8H2O hydrated phosphate containing hydroxyl
Specific gravity: 1.8 to 2.2
Hardness: 3 to 4
Streak: White, lightly tinted
Colour: Colourless, milk-white, lightly tinted blue, green or yellow at times; brown, reddish-brown, or red due to wüstite inclusions; colourless to brown in transmitted light
Solubility: Easily soluble in acids
Environments:

Metamorphic environments

Evansite is a secondary phosphate mineral that forms as a derivative of guano, usually in the form of cave fillings in graphite-containing deposits, gneiss and coal strata. Associated minerals include variscite, allophane and limonite.
Common impurities: Cu,Pb

Faujasite

Faujasite is three mineral species:
Faujasite-Ca, (Ca,Na,Mg)2(Si,Al)12O24.15H2O
Faujasite-Mg, (Mg,Na,K,Ca)2(Si,Al)12O24.15H2O
Faujasite-Na, (Na,Ca,Mg)2(Si,Al)12O24.15H2O
They are tectosilicates (framework silicates), zeolite group
Specific gravity: 1.92 to 1.93
Hardness: 4½ to 5
Streak: White
Colour: Colourless, white, pale brown
Environments:

Sedimentary environments
Basaltic cavities

Faujasite usually occurs in cavities in basaltic volcanics, and also as an alteration product of volcanic tuff.

Fayalite

Formula: Fe2+2(SiO4) nesosilicate (insular SiO4 groups), olivine group
Properties of fayalite:
Specific gravity: 4.392
Hardness: 6½
Streak: White
Colour: Green, yellow, brown
Solubility: Insoluble in water and nitric acid; soluble in hydrochloric acid forming an insoluble silica gel
Environments:

Volcanic igneous environments

Alteration

fayalite and H2O to magnetite, SiO2 and H2
3Fe2+2(SiO4) + 2H2O &38594; Fe2+Fe3+2O4 + 3SiO2 + 2H2
This reaction is highly exothermic.

fayalite, H2O and O2 to cronstedtite and magnetite
6Fe2+2(SiO4) + 6H2O + ½O2 = 3Fe3Si2O5(OH)4 + Fe2+Fe3+2O4

fayalite, oxygen and H2O to hematite and silicic acid
2Fe2SiO4 + O2 + 4H2O → 2Fe2O3 + 2H4SiO4
On prolonged exposure to the air Fe2+ compounds are oxidised to Fe3+ compounds according to reactions such as the one above.

fayalite, SiO2 and H2O to grunerite
7Fe2+2(SiO4) + 9SiO2 + 2H2O → 2Fe2+2Fe2+5Si8O22(OH)2
Fayalite may undergo partial regression to grunerite according to the above reaction.

ferrosilite to fayalite and quartz
Fe2Si2O6 ⇌ Fe2SiO4 + SiO2
Ferrosilite is unstable at pressure less than about 15 kbar

forsterite, fayalite, H2O and CO2 to serpentine, magnetite and methane
18 Mg2SiO4 + 6Fe2SiO4 + 26H2O + CO2 → 12Mg3Si2O5(OH)4 + 4Fe3O4 + CH4

siderite and quartz to fayalite and CO2
2Fe(CO3) + SiO2 = Fe2+2(SiO4) + 2CO2

Common impurities: Mn

Feldspar

Feldspars comprise a group of rock-forming tectosilicate minerals that make up as much as 60% of the Earth's crust. They are divided into two groups, K-feldspar, which are rich in potassium, and plagioclase feldspar feldspars that contain no potassium.
The major K-feldspar are orthoclase, sanidine, microcline and anorthoclase.
The major plagioclase feldspars are albite, oligoclase, andesine, labradorite and anorthite.
Feldspars are primary minerals; they are essential constituents of granite, syenite, diorite, gabbro, rhyolite, trachyte, andesite, basalt and , sandstone.
Feldspars are common constituents of phyllite and gneiss, and medium constituents of quartzolite.
K-feldspar are minerals of the greenschist and amphibolite facies.

Feldspathoid

Feldspathoids form a family of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. They occur in rare and unusual types of igneous rocks, and are not found in rocks containing primary quartz.
Feldspathoids are common constituents of basalt.
They also may be found in diorite and gabbro.
Nepheline is the commonest feldspathoid.

Ferberite

Formula: Fe2+(WO4) anhydrous tungstate
A complete solid solution exists between ferberite and hübnerite.
Specific gravity: 7.51
Hardness: 4 to 4½
Streak: Black to brownish-black
Colour: Black
Solubility: Easily fusible. Slowly decomposed by hot concentrated sulphuric or hydrochloric acid. Decomposed by aqua regia with the separation of tungstic oxide.
Environments:

Pegmatites
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Ferberite occurs in hydrothermal veins, medium temperature metamorphic rocks and granitic pegmatites immediately associated with granitic intrusive rocks; it also occurs in alluvial and residual deposits.
In high temperature (hypothermal) hydrothermal veins it is associated with cassiterite, arsenopyrite, apatite, tourmaline, topaz, fluorite, specular hematite, molybdenite and bismuth. In moderate temperature (mesothermal) veins it is associated with cassiterite and sulphides, scheelite, bismuthinite and siderite.

Localities

Australia

At Rumsby's mine, New South Wales, ferberite is the main ore mineral, associated with a granite intrusion, and it is commmonly intergrown with bismuth, arsenopyrite and fluorite. Some ferberite has altered to secondary scheelite.

Common impurities: Nb,Ta,Sc,Sn

Ferrierite

Ferrierite three minerals:
Ferrierite-K, (K,Na)5(Si31Al5)O72.18H2O
Ferrierite-Mg, [Mg2(K,Na)2Ca0.5](Si29Al7)O72.18H2O
Ferrierite-Na, (Na,K)5(Si31Al5)O72.18H2O
They are tectosilicate (framework silicates), zeolite group
Specific gravity: 2.06 to 2.23
Hardness: 3 to 3½
Streak: White
Colour: Colourless, white, pink, orange, red due to Fe3+
Environments:

Metamorphic environments
Sedimentary environments
Basaltic cavities

Ferrierite occurs in cavity fillings in basaltic rocks and as a diagenetic mineral in rhyolite tuff, as a result of hydration reactions. It also occurs in metamorphic rocks.

Ferro-actinolite

Formula: ☐Ca2(Mg2.5-0.0Fe2+2.5-5.0)Si8O22 (OH)2
Mg/(Mg+Fe2+) < 0.5, inosilicate (chain silicate)
Specific gravity: 3.24 to 3.48
Hardness: 5 - 6
Streak: greenish white
Colour: black-green, dark green
Environments

Metamorphic environments

Ferro-actinolite occurs in iron-rich greenschist and blueschist facies metamorphic rocks and in metamorphosed iron formations. In regional metamorphic environments it is associated with hedenbergite. In contact metamorphic environments it is associated with andradite and ilvaite. In iron formations it is associated with cummingtonite, quartz, magnetite, riebeckite, biotite and hematite.

Alteration

ferro-actinolite to hedenbergite, grunerite, quartz and H2O
7Ca2Fe2+5Si8O22(OH)2 → 14CaFe2+Si2O6 + 3Fe2+2Fe2+5 Si8O22(OH)2 + 4SiO2 + 4H2O
In some calc-silicate rocks hedenbergite is the product of metamorphism of iron-rich sediments, probably due to the instability of ferro-actinolite with rising temperature. The association of hedenbergite and grunerite has been widely described, and its formation may be due to the above reaction.

ferro-actinolite, calcite and quartz to hedenbergite, CO2 and H2O
Ca2Fe2+5Si8O22(OH)2 + 3CaCO3 + 2SiO2 ⇌ 5CaFe2+Si2O6 + 3CO2 + H2O
In some calc-silicate rocks hedenbergite is the product of metamorphism of iron-rich sediments, according to the above reaction, probably due to the instability of ferro-actinolite with rising temperature.

Common impurities: Ti,Al,Mn,Na,K,F,P

Ferro-anthophyllite

Formula: Fe2+2Fe2+2Si8O22(OH)2 inosilicate (chain silicate) amphibole
Specific gravity:
Hardness: 5½ to 6
Streak: White to greyish white
Colour: Clove-brown to dark brown, grey to white, pale green

Ferro-gedrite

Formula: ☐Fe2+2(Fe2+3Al2) (Si6Al2)O22(OH)2 inosilicate (chain silicate) amphibole
Specific gravity:
Hardness: 5½ to 6
Streak: White
Colour: Pale greenish-grey to brown
Solubility:
Environments:

Metamorphic environments

Ferrogedrite exists in low temperature, high pressure contact metamorphic geologic settings and remains stable up to 600°C-800°C due to its iron content.

Alteration

gedrite-ferro-gedrite and quartz to enstatite-ferrosilite, Fe-rich cordierite and H2O
2(Mg,Fe2+)5Al4Si6O22(OH)2 + 4Si2 → 3(Mg,Fe2+)2Si2O6 + 2(Mg,Fe2+)2Al4Si5O18 + 2H2O
In the pyroxene-hornfels facies enstatite-ferrosilite may develop from gedrite-ferro-gedrite according to the above reaction.

Common impurities: Ti,Mn,Ca,Na,K,F

Ferrosilite

Formula: Fe2+2Si2O6 inosilicate (chain silicate) pyroxene group
Specific gravity:
Hardness: 5 to 6
Streak: Pale grey brown
Colour: Dark brown to black

Plutonic igneous environments
Volcanic igneous environments
Metamorphic environments

Ferrosilite is found in basic and ultrabasic igneous rocks and also in high-grade metamorphic rocks, such as the granulite facies. Ferrosilite is common in metamorphosed iron formation in association with grunerite.

Alteration

augite and andalusite to enstatite-ferrosilite and anorthite
2Ca(Fe,Mg)Si2O6 + 2Al2SiO5 → (Mg,Fe2+)2Si2O6 + 2Ca(Al2Si2O8)

biotite and quartz to enstatite-ferrosilite, orthoclase and H2O
K(Mg,Fe)3(AlSi3O10)(OH)2 + 3SiO2 → 3(Mg,Fe2+)SiO3 + KAlSi3O8 + H2O Enstatite-ferrosilite may develop from the breakdown of biotite according to the above reaction.

chlorite and quartz to enstatite- ferrosilite, Fe-rich cordierite and H2O
(Mg,Fe2+)4Al4Si2O10(OH)8 + 5SiO2 → 2(Mg,Fe2+)SiO3 + (Mg,Fe2+2)2Al4Si5O18 + 4H2O
Enstatite-ferrosilite also occurs in medium grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content according to the above equation.

Fe-rich cordierite and diopside- hedenbergite to enstatite- ferrosilite, anorthite and quartz
(Mg,Fe)2 Al4Si5O18 + 2Ca(Mg,Fe)Si2O6 = 4(Mg,Fe2+)SiO3 + 2Ca(Al2Si2O8) + SiO2

cummingtonite-grunerite and olivine to enstatite-ferrosilite and H2O
(Fe,Mg)7Si8O22(OH)2 + (Mg,Fe)2SiO4 ⇌ 9(Mg,Fe2+)SiO3 + H2O

diopside-hedenbergite and CO2 to enstatite-ferrosilite, calcite and quartz
Ca(Mg,Fe)Si2O6 + CO2 → (Mg,Fe2+)SiO3 + CaCO3 + SiO2

enstatite-ferrosilite and H2O to serpentine and quartz
6(Mg,Fe2+)SiO3 + 4H2O ⇌ (Fe,Mg)6Si4O10(OH)8 +2SiO2

enstatite-ferrosilite and andalusite to Fe-rich cordierite and spinel- hercynite
5(Mg,Fe2+)SiO3 + 5 Al2SiO5 → 2(Mg,Fe2+)2Al4Si5O18 + (Mg,Fe2+)Al2O4
In medium-grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content, the association of andalusite with enstatite-ferrosilite is excluded by the above reaction.

enstatite-ferrosilite, andalusite and SiO2 to Fe-rich cordierite
2(Mg,Fe2+)SiO3 + 2Al2SiO5 + SiO2 → (Mg,Fe2+)2Al4Si5O18
In medium-grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content, the association of andalusite with enstatite-ferrosilite is excluded by the above reaction.

enstatite-ferrosilite, diopside- hedenbergite, albite, anorthite and H2O to amphibole and quartz
3(Mg,Fe2+)SiO3 + Ca(Mg,Fe2+)Si2O6 + NaAlSi3O8 + Ca(Al2Si2O8) + H2O ⇌ NaCa2(Mg,Fe)4Al(Al2O6)O22(OH)2 + 4SiO2 This reaction represents metamorphic reactions between the granulite and amphibolite facies.

enstatite-ferrosilite, Fe-rich diopside and Fe, Cr-rich spinel to garnet and olivine
2(Mg,Fe2+)SiO3 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4

enstatite-ferrosilite, K-feldspar and H2O to biotite and quartz
3(Mg,Fe2+)SiO3 + K(AlSi3O8) + H2O ⇌ K(Mg,Fe)3(AlSi3O10)(OH)2+ 3SiO2
The forward reaction leads to an amphibolite facies assemblage.

enstatite-ferrosilite, SiO2 and H2O to cummingtonite- grunerite
7(Mg,Fe2+)SiO3 + SiO2 + H2O ⇌ (Fe,Mg)7Si8O22(OH)2

ferrosilite to fayalite and quartz
Fe2Si2O6 ⇌ Fe2SiO4 + SiO2
Ferrosilite is unstable at pressure less than about 15 kbar

gedrite- and quartz to enstatite-ferrosilite, Fe-rich cordierite and H2O
(Mg,Fe2+)5Al4Si6O22(OH)2 + 2Si2 → 3(Mg,Fe2+)SiO3 + (Mg,Fe2+)2Al4Si5O18 + H2O In the pyroxene-hornfels facies enstatite-ferrosilite may develop from gedrite-ferro-gedrite according to the above reaction.

olivine and CO2 to enstatite-ferrosilite and magnesite-siderite
(Mg,Fe)2SiO4 + CO2 → (Mg,Fe2+)SiO3 + (Mg,Fe)CO3

olivine and quartz to enstatite-ferrosilite
(Mg,Fe)2SiO4 + SiO2 → 2(Mg,Fe2+)SiO3

Common impurities: Ca,Na,K,Al,Co,Ni,Mn,Ti,Cr

Fleischerite

Formula: Pb3Ge(SO4)2(OH)6.3H2O hydrated sulphate containing hydroxyl

Fluorite

Formula: CaF2 fluoride
Specific gravity: 3.18
Hardness: 4
Streak: White
Colour: Colourless, white, purple, green, blue, yellow, pink, red
Solubility: Slightly soluble in hydrochloric acid; moderately soluble in sulphuric acid; slightly soluble in water
Melting point 1403°C, boiling point 2500°C.
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites
Sedimentary environments
Hot spring deposits
Hydrothermal environments

Fluorite is a common and widely distributed mineral; it mainly occurs as a pore-filling mineral in limestone and dolostone, and in mesothermal (moderate temperature) and hypothermal (high temperature) hydrothermal vein deposits associated with lead and silver ores. Less often it may be found as a primary mineral in igneous rocks and pegmatites, where it is a late-stage mineral following deposition of beryl, topaz and tourmaline. In carbonatites it is associated with albite and pyrite. It also may be precipitated at hot springs.

Fluorite may be found in granite, quartzolite and dolostone.

When fluorite occurs as a cavity fill in carbonate rocks it is usually associated with calcite, dolomite, anhydrite, gypsum and sulphur.
In hydrothermal vein deposits, fluorite may be found with calcite, dolomite, baryte, galena, sphalerite and molybdenite.

Pseudomorphs of quartz after fluorite are common. Fluorite also forms pseudomorphs after calcite, baryte and galena.

Localities

Australia

At Rumsby's mine, New South Wales, Australia, indications are that fluorite was formed at temperatures between 451 and 462oC in intersecting vein systems in granite. The paragenetic sequence included early stage smoky quartz, arsenopyrite, ferberite, bismuth, monazite, fluorite, beryl, ilmenite, adularia, muscovite and tourmaline group minerals. A later stage precipitated quartz, muscovite, chalcopyrite, pyrite and chlorite group minerals. Secondary alteration replacement minerals included scheelite after ferberite, chalcopyrite, pyrrhotite and cubanite, hematite and rutile after ilmenite and covellite after chalcopyrite.

USA

At the Findlay Arch Mineral District spanning parts of Ohio, Michigan and Indiana, fluorite occurs together with calcite and celestine in Silurian and Devonian limestone. These minerals formed in cavities after the rock was laid down. The dark brown fluorite from this locality is coloured by inclusions of bituminous particulates, and fluoresces blue under shortwave radiation.

Common impurities in fluorite: Y,Ce,Si,Al,Fe,Mg,Eu,Sm,O,ORG,Cl,TR

Forsterite

Formula: Mg2SiO4 nesosilicate (insular SiO4 groups), olivine group
Specific gravity: 3.222
Hardness: 6½ to 7
Streak: White
Colour: Yellow, green, brown, black
Melting point: About 1,900oC at atmospheric pressure
Solubility: Insoluble in water and sulphuric acid; soluble in hydrochloric and nitric acid forming an insoluble silica gel
Environments:

Volcanic igneous environments
Metamorphic environments

Forsterite is a primary mineral occurring in mafic and ultramafic igneous rocks, and also in metamorphosed impure dolostone, and it is also found as glassy grains in stony and stony-iron meteorites. It occurs in the mantle above a depth of about 400 km. If the melt is low in silica, but above average in magnesium and iron, olivine will crystallise out.
Forsterite may be found in dolostone and skarn.
It is often associated with pyroxene, plagioclase feldspar, magnetite, corundum, chromite and serpentine.
Forsterite is a mineral of the blueschist greenschist, amphibolite and granulite facies.

Alteration

During the progressive metamorphism of silica-rich dolostones the following approximate sequence of mineral formation is often found, beginning with the lowest temperature product: talc, tremolite, diopside, forsterite, wollastonite, periclase, monticellite

anthophyllite and forsterite to enstatite and H2O
2☐Mg2Mg5Si8O22(OH)2 + 2Mg2SiO4 ⇌ 9Mg2Si2O6 + 2H2O
At 2 kbar pressure the equilibrium temperature is about 690oC (pyroxene-hornfels facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures.

antigorite to forsterite, talc and H2O
5Mg3Si2O5(OH)4 = 6Mg2SiO4 + Mg3Si4O10(OH)2 + 9H2O
This reaction may occur in olivine-diopside- antigorite schist within the aureole of the tonalite in the southern Bergell Alps, Italy, at a higher grade of metamorphism than that which produces forsterite and tremolite.
At 10 kbar pressure the equilibrium temperature is about 600oC (amphibolite facies), with equilibrium to the right at higher temperatures and to the left at lower temperatures (for the same pressure).

antigorite and calcite to forsterite, diopside, CO2 and H2O
3Mg3Si2O5(OH)4 + CaCO3 → 4Mg2SiO4 + CaMgSi2O6 + CO2 +6 H2O
This reaction has been found to occur in antigorite schist at about 3 kbar pressure and 400 to 500oC (greenschist facies).

antigorite and magnesite to forsterite, CO2 and H2O
Mg3Si2O5(OH)4 + MgCO3 → 2Mg2SiO4 + CO2 + 2H2O

brucite and antigorite to forsterite and H2O
Mg(OH)2 + Mg3Si2O5(OH)4 ⇌ 2Mg2SiO4 + 3H2O
The equilibrium temperature for this reaction at 8 kbar pressure is about 450oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures. The reaction also may occur in the albite-epidote-hornfels and blueschist facies.

corundum and forsterite to spinel and enstatite
2Al2O3 + 2Mg2SiO4 ⇌ 2MgAl2O4 + Mg2Si2O6
At 10 kbar pressure the equilibrium temperature is about 570oC (amphibolite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

diopside and antigorite to forsterite, Mg-rich tremolite and H2O
2CaMgSi2O6 + 5Mg3Si2O5(OH)4 ⇌ 6Mg2SIO4 + Ca2Mg5Si8O22(OH)2 + 9H2O
At 10 kbar pressure the equilibrium temperature is about 580oC (amphibolite facies).

diopside and dolomite to forsterite, calcite and CO2
CaMgSi2O6 + 3CaMg(CO3)2 → 2Mg2SiO4 + 4CaCO3 + 2CO2
This is a high-grade metamorphic change occurring at temperature in excess of 600oC.

diopside, forsterite and calcite to monticellite and CO2
CaMgSi2O6 + Mg2SiO4 + 2CaCO3 → 3CaMgSiO4 + 2CO2
This reaction requires a high temperature.

dolomite and quartz to forsterite, calcite and CO2
2CaMg(CO3)2 + SiO2 → Mg2SiO4 + 2CaCO3 + 2CO2 In siliceous dolostone dolomite and quartz may react to form either diopside or forsterite, with diopside forming at a lower temperature than forsterite.

dolomite and tremolite to forsterite, calcite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 11CaMg(CO3)2 → 8Mg2SiO4 + 13CaCO3 + 9CO2 + H2O

dolomite, tremolite and forsterite to diopside, enstatite and H2O
Ca2Mg5Si8O22(OH)2 + Mg2SiO4 ⇌ 2CaMgSi2O6 + H2O
At a pressure of 4 kbar the equilibrium temperature is about 840oC (granulite facies).

enstatite and H2O to forsterite and cummingtonite
9MgSiO3 + H2O = Mg2SiO4 + Mg2Mg5Si8O22(OH)2
Cummingtonite may be formed by retrograde metamorphism according to the above reaction.

enstatite and calcite to forsterite, diopside and CO2
3Mg2Si2O6 + 2CaCO3 ⇌ 2Mg2SiO4 + 2CaMgSi2O6 + 2CO2 Enstatite is uncommon in the more calcareous hornfels due to reactions such as the above.

Al-rich enstatite and Al-rich diopside to forsterite, enstatite, diopside and anorthite
Mg9Al2Si9O30 + Ca5Mg4Al2Si9O30 ⇌ 2Mg2SiO4 + 3Mg2Si2O6 + 3CaMgSi2O6 + 2Ca(Al2Si2O8)
This reaction occurs at fairly low temperature and pressure.

enstatite and spinel to forsterite and cordierite
5Mg2Si2O6 + 2MgAl2O4 ⇌ 5Mg2SiO4 + Mg2Al4Si5O18
At 4 kbar pressure the equilibrium temperature is about 715oC (amphibolite facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

forsterite and CO2 to enstatite and magnesite
Mg2SiO4 + CO2 ⇌ MgSiO3 + MgCO3

forsterite and H2O to serpentine and brucite
2Mg2SiO4 + 3H2O ⇌ Mg3Si2O5(OH)4 + Mg(OH)2
The forward reaction is highly exothermic. At 5 kbar pressure the equilibrium temperature is about 420°C (greenschist facies).

forsterite, SiO3 and H2O to serpentine
3Mg2SiO4 + SiO2 + 4H2O → 2Mg3Si2O5 (OH)4
This reaction is highly exothermic.

forsterite and åkermanite to diopside and monticellite
Mg2SiO4 + 2Ca2MgSi2O7 → CaMgSi2O6 + 3CaMg(SiO4)

forsterite and anorthite to clinoenstatite, diopside and spinel
2Mg2SiO4 + CaAl2Si2O8 ⇌ 2MgSiO3 + CaMgSi2O6 + MgAl2O4

forsterite and anorthite to enstatite, diopside and spinel
2Mg2SiO4 + Ca(Al2Si2O8) = Mg2Si2O6 + CaMgSi2O6 + MgAl2O4

forsterite, calcite and quartz to diopside and CO2
Mg2SiO4 + 2CaCO3 + 3SiO2 → 2CaMgSi2O6 + 2CO2
In high temperature environments with excess SiO2 diopside may form according to the above reaction.

forsterite, calcite and quartz to monticellite and CO2
Mg2SiO4 + 2CaCO3 + SiO2 → 2CaMg(SiO4) + 2CO2

forsterite, diopside and calcite to monticellite and CO2
Mg2SiO4 + CaMgSi2O6 + 2 CaCO3 ⇌ 3CaMg(SiO4) + 2 CO2
This reaction occurs during contact metamorphism of magnesian limestone.

forsterite, dolomite and H2O to calcite, hydroxylclinohumite and CO2
4Mg2SiO4 + CaMg(CO3)2 + H2O → Mg9(SiO4)4(OH)2 +CaCO3 + CO2
A forsterite-clinohumite assemblage in the silica-rich dolomite in the aureole of the Alta granodiorite in Utah, USA, is probably due to the above reaction.

forsterite, enstatite and H2O to serpentine
2Mg2SiO4 + Mg2Si2O6 + 4H2O → 2Mg3Si2O5(OH)4
Serpentine is not stable in the presence of carbon dioxide, and may further react with it to form talc and magnesite.

forsterite, fayalite, H2O and CO2 to serpentine, magnetite and methane
18 Mg2SiO4 + 6Fe2SiO4 + 26H2O + CO2 → 12Mg3Si2O5(OH)4 + 4Fe3O4 + CH4

forsterite, kyanite and quartz to cordierite
Mg2SiO4 + 2Al2OSiO4 + 2SiO2 ⇌ Mg2Al4Si5O18
At 6 kbar pressure the equilibrium temperature is about 400oC (greenschist facies).

forsterite and quartz to enstatite
Mg2SiO4 + SiO2 → 2MgSiO3
Forsterite is not stable in the presence of free SiO2 and will react with it to form enstatite according to the above reaction.

forsterite and talc to anthophyllite and H2O
4Mg2SiO4 + 9Mg3Si4O10(OH)2 ⇌ 5Mg2Mg5Si8O22(OH)2 + 4H2O
At 2 kbar pressure the equilibrium temperature is about 650oC (pyroxene-hornfels facies), with equilibrium to the right at higher temperatures and to the left at lower temperatures (for the same pressure).

forsterite and talc to enstatite and H2O
Mg2SiO4 + Mg3Si4O10(OH)2 ⇌ 5MgSiO3 + H2O
At 10 kbar pressure the equilibrium temperature is about 680oC (amphibolite facies), with equilibrium to the right at higher temperatures and to the left at lower temperatures (for the same pressure).

labradorite, albite, forsterite and diopside to omphacite, garnet and quartz
3CaAl2Si2O8 + 2Na(AlSi3O8) + 3Mg2SiO4 + nCaMgSi2O6 → (2NaAlSi2O6 + nCaMgSi2O6) + 3(CaMg2)Al2(SiO4)3 + 2SiO2
This reaction occurs at high temperature and pressure.

monticellite and CO2 to åkermanite, forsterite and calcite
3CaMgSiO4 + CO2 ⇌ Ca2MgSi2O7 + Mg2O7 + CaCO3
At 4.3 kbar pressure the equilibrium temperature is about 890oC (granulite facies).

monticellite and diopside to åkermanite and forsterite
3CaMgSiO4 + CaMgSi2O6 ⇌ 2Ca2MgSi2O7 + Mg2O7
Monticellite is stable below 890oC at pressure of about 4.3 kbar (granulite facies).

nepheline and diopside to melilite, forsterite and albite
3NaAlSiO4 + 8CaMgSi2O6 ⇌ 4Ca2MgSi2O7 + 2Mg2SiO4 + 3NaAlSi3O8
This reaction is in equilibrium at about 1180oC, with lower temperatures favouring the forward reaction.

serpentine and brucite to forsterite and H2O
Mg3Si2O5(OH)4 + Mg(OH)2 ⇌ 2Mg2SiO4 + 3H2O
This reaction can proceed in either direction, depending on the external conditions. Early formation of forsterite.

serpentine and diopside to forsterite and talc
5Mg3Si2O5(OH)4 ⇌ 6Mg2SiO4 + Mg3Si4O10(OH)2 + 9H2O
In olivine-diopside- antigorite schist within the aureole of the tonalite in the southern Bergell Alps, Italy, at a higher grade of metamorphism than that which produces forsterite and tremolite.

serpentine and diopside to tremolite, forsterite and H2O
5Mg3Si2O5(OH)4 + 2CaMgSi2O6 ⇌ Ca2Mg5Si8O22(OH)2 + 6Mg2SiO4 + 9H2O + H2O
In lower grade assemblages associated with contact and regional metamorphism serpentine may form tremolite and forsterite according to the above reaction.

Fe and Cr-rich spinel , diopside and enstatite to forsterite, anorthite and chromite
MgFeAl2Cr2O8 + CaMgSi2O6 + Mg2Si2O6 ⇌ 2Mg2SiO4 + Ca(Al2Si2O8) + Fe2+Cr2O4
This reaction occurs at fairly low temperature and pressure.

spinel and tremolite to forsterite and magnesio-hornblende
MgAl2O4 + Ca2Mg5Si8O22(OH)2 ⇌ Mg2SiO4 + Ca2(Mg4Al)(Si7Al)O22(OH)2
This reaction occurs in some strongly metamorphosed serpentinite

tremolite and dolomite to forsterite, calcite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 11CaMg(CO3)2 → 8Mg2SiO4 + 13CaCO3 + 9CO2 + H2O

tremolite and forsterite to diopside, enstatite and H2O
Ca2Mg5Si8O22(OH)2 + Mg2SiO4 ⇌ 2CaMgSi2O6 + H2O
The equilibrium temperature for this reaction at 4 kbar pressure is 840oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

Common impurities: Fe

Franklinite

Formula: ZnFe3+2O4
Multiple oxide, spinel group
Specific gravity: 5.2
Hardness: 5½ to 6½
Streak: Reddish brown to black
Colour: Black
Solubility: Soluble in hydrochloric acid
Environments:

Metamorphic environments

Franklinite occurs in a zinc-rich orebody of marine carbonate sediments, weathered and later metamorphosed at high temperature. Associated with zincite, willemite, calcite, andradite, manganosite, rhodochrosite, gahnite, magnetite, rhodonite, hausmannite, hetaerolite, jacobsite, braunite, sarkinite, berzeliite and hematite.
Common impurities: Mn2+, Mn3+, Fe2+, Ti,Al,Ca

Gahnite

Formula: ZnAl2O4 multiple oxide, spinel group, gahnite-hercynite series, gahnite-spinel series.
Specific gravity: 4.57
Hardness: 7½ to 8
Streak: Grey
Colour: Dark blue-green, yellow, brown, black
Solubility:
Environments:

Pegmatites
Metamorphic environments

Gahnite occurs in crystalline schist, in granite pegmatites especially those rich in lithium, and in contact metamorphosed limestone. It also occurs in high temperature replacement ore deposits in schist or marble.

Common impurities: Fe,Mg

Galaxite

Formula: Mn2+Al2O4 multiple oxide, spinel group
Specific gravity: 4.234
Hardness: 7½
Streak: Red-brown
Colour: Black or mahogany red
Environments:

Metamorphic environments

At the Bald Knob Mine, North Carolina, galaxite occurs in carbonate-rich, silica undersaturated parts of a metamorphosed manganese deposit. It is commonly intergrown with alleghanyite, and further associated with tephroite, quartz, magnetite and jacobsite. The minerals here have formed under amphibolite facies metamorphic conditions.

Galena

Formula: PbS sulphide
Specific gravity: 7.2 to 7.6
Hardness: 2½
Streak: Lead-grey
Colour: Lead-grey
Solubility: Slightly soluble in hydrochloric and nitric acids
Environments:

Metamorphic environments
Hydrothermal environments

Galena is a common primary mineral, found in hypothermal (high temperature) and mesothermal (moderate temperature) veins and in contact metamorphic deposits.
In hydrothermal veins it is often associated with anglesite, baryte, bornite, calcite, cerussite, chalcopyrite, dolomite, fluorite, marcasite, pyrite, quartz and sphalerite.

Alteration

In the oxidation zone of epithermal (low temperature) veins initially pyrite is oxidised to ferric sulphate, which is itself a strong oxidising agent. The ferric sulphate then reacts with galena to form anglesite.
Oxidation of pyrite:
pyrite + oxygen + H2O → ferrous sulphate + sulphuric acid
FeS2 + 7O + H2O → FeSO4 + H2SO4
The ferrous (divalent) sulphate readily oxidises to ferric (trivalent) sulphate and ferric hydroxide
ferrous sulphate + oxygen + H2O → ferric sulphate + ferric hydroxide
6FeSO4 + 3O + 3H2O → 2Fe2(SO4)3 + 2Fe(OH)3

galena, ferric sulphate, water and oxygen to anglesite, ferrous sulphate and sulphuric acid
PbS + Fe2(SO4)3 + H2O + 3O → PbSO4 + 2FeSO4 + H2SO4
Galena is oxidised to anglesite and ferric iron is reduced to ferrous iron.

Galena may also dissolve in carbonic acid from percolating rainwater to form hydrogen sulphide, which is then oxidised to form anglesite.

galena and carbonic acid to Pb2+, hydrogen sulphide and HCO3-
PbS + 2H2CO3 → Pb2+ + H2S + 2HCO3-
then hydrogen sulphide, oxygen, Pb2+ and HCO3- to anglesite and carbonic acid
H2S + 2O2 + Pb2+ + 2HCO3- → PbSO4 + 2H2CO3

galena and oxygen to anglesite
In air, at outcrops of galena,
PbS + 2O2 → PbSO4
At ordinary temperatures the equilibrium is displaced far to the right, and the apparent stability of galena is a result of the slowness of the oxidation.

In the oxidation zone of epithermal veins galena alters to anglesite or cerussite depending on the acidity. Cerussite forms in more basic (alkaline) environments than anglesite.
During the progressive weathering of assemblages of supergene lead minerals anglesite disappears first, then cerussite, and finally only pyromorphite, mimetite and vanadinite persist.

Common impurities: Ag,Cu,Fe,Bi

Gangue

Gangue is the valueless part of an ore, with no economic value.

Ganophyllite

Formula: (K,Na)xMn2+6(Si,Al)10O24(OH)4.nH2O (x=1-2; n=7-11)
Phyllosilicate (sheet silicate), ganophyllite group
Specific gravity: 2.84 to 2.88
Hardness: 4 to 4½
Streak: Brownish yellow
Colour: Brownish yellow, cinnamon-brown
Solubility: Gelatinises in acids
Environments:

Metamorphic environments

Ganophyllite occurs in manganese-rich portions of metamorphosed zinc-manganese mineral deposits.

At Mont Saint-Hilaire, Quebec, Canada, ganophyllite occurs with astrophyllite and labuntovite.

At the Molinello mine, Italy, ganophyllite is associated with parsettensite and caryopilite

At Harstigen mine, Sweden, ganophyllite is associated with calcite, rhodonite, caryopilite, baryte, lead, garnet, manganoanbiotite and pyrophanite.

At Franklin, New Jersey, USA, ganophyllite is associated with rhodonite, willemite, bustamite, axinite, clinohedrite, datolite, roeblingite and charlesite.

Common impurities: Fe,Zn,Pb,Ca,Ba

Garnet

The garnet group is a group of nesosilicate (insular SiO4 groups) minerals including almandine, pyrope, spessartine, andradite, grossular and uvarovite.
Environments:

Plutonic igneous environments
Pegmatites
Sedimentary environments
Placer deposits
Metamorphic environments (typical)
Hydrothermal environments

Garnet is a common and widely distributed mineral occurring abundantly in some metamorphic rocks, and as an accessory constituent in some igneous rocks. It is also found in sedimentary environments including placers, and in hydrothermal replacement lodes.
Garnet may be found in granite, diorite, skarn, schist and gneiss.
Its most characteristic occurrence is in mica schist, hornblende schist and gneiss.
It is characteristic of the amphibolite facies, and it is also a mineral of the greenschist, granulite, blueschist and eclogite facies.
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid

Alteration

albite, diopside and magnetite to aegirine, garnet and quartz
2Na(AlSi3O8) + CaMgSi2O6 + Fe2+Fe3+2O4 ⇌ 2NaFe3+Si2O6 + Si2O6 + CaMgFe2+Al2(SiO4)3 + SiO2
This reaction may occur in blueschist facies rocks in Japan.

amphibole, chlorite, paragonite, ilmenite, quartz and calcite to garnet, omphacite, rutile, H2O and CO2
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + Mg5Al(AlSi3O10)(OH)8 + 3NaAl2(Si3Al)O10(OH)2 + 4Fe2+Ti4+O3 + 9SiO2 + 4CaCO3 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 8H2O + 4CO2 In low-grade rocks relatively rich in calcite the garnet-omphacite association may be due to reactions such as the above.

amphibole, clinozoisite, chlorite, albite, ilmenite and quartz to garnet, omphacite, rutile and H2O
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + 2Ca2Al3[Si2o7][SiO4]O(OH) + Mg5Al(AlSi3O10)(OH)8 + 3NaAlSi3O8 + 4Fe2+Ti4+O3 + 3SiO2 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 6H2O In low-grade rocks relatively poor in calcite the garnet-omphacite association may be developed by the above reaction.

augite, albite, pyroxene, anorthite and ilmenite to omphacite, garnet, quartz and rutile
2MgFe2+Si2O6 + Na(AlSi3O8) + Ca2Mg2Fe2+Fe3+AlSi5O18 + 2Ca(Al2Si2O8) + 2Fe2+Ti4+O3 → NaCa2MgFe2+Al(Si2O6)3 + (Ca2Mg3Fe2+4)(Fe3+Al5)(SiO4)9 + SiO2 + 2TiO2 This reaction occurs at high temperature and pressure.

enstatite-ferrosilite, Fe-rich diopside and Fe, Cr-rich spinel to garnet and olivine
2(Mg,Fe2+)SiO3 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4

hypersthene, augite and Fe and Cr-rich spinel to garnet and olivine
2(Mg,Fe)SiO3 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4

labradorite, albite, forsterite and diopside to omphacite, garnet and quartz
3CaAl2Si2O8 + 2Na(AlSi3O8) + 3Mg2SiO4 + nCaMgSi2O6 → (2NaAlSi2O6 + nCaMgSi2O6) + 3(CaMg2)Al2(SiO4)3 + 2SiO2
This reaction occurs at high temperature and pressure.

muscovite, biotite and SiO2 to K-feldspar, garnet and H2O
KAl2(AlSi3O10)(OH)2 + K(Fe2+,Mg)3(AlSi3O10)(OH)2 + 3SiO2 → 2KAlSi3O8 + (Fe2+,Mg)3Al2(SiO4)3 + 2H2O

muscovite and garnet to biotite, sillimanite and quartz
KAl2(AlSi3O10)(OH)2 + (Fe2+,Mg)3Al2(SiO4)3 → K(Fe2+,Mg)3(AlSi3O10)(OH)2 + 2Al2SiO5 + SiO2
Muscovite is unstable in combination with garnet.

meionite (scapolite series) and augite to garnet, calcite and quartz
Ca4Al6O24(CO3) + 3Ca(Mg,Fe2+)Si2O6 ⇌ 3Ca2(Mg,Fe2+)Al2(SiO4)3 + CaCO3 + 3SiO2

Garronite

Garronite is a series with end members:
Garronite-Ca: Ca3(Al6Si10O32).14H2O
Garronite-Na: Na6(Al6Si10O32).8.5H2O
These minerals are tectosilicates (framework silicates), zeolite group
Specific gravity: 2.13 to 2.18
Hardness: 4½ to 5
Streak: White
Colour: Colourless, white
Garronite is most common in vesicles in basalt and other mafic rocks, often overgrown by or associated with phillipsite, and also as epitaxial overgrowths on phillipsite. At Mont St Hilaire, Canada, it occurs in some metamorphic rocks and in sodalite xenoliths.

Gaylussite

Formula: Na2Ca(CO3)2.5H2O hydrated normal carbonate
Specific gravity: 2.367
Hardness: 3 to 3½
Streak: White
Colour: Colourless, white
Solubility: Soluble with effervescence in acids. Slightly soluble in water
Environments

Sedimentary environments

Gaylussite is usually found in soda lakes with natron, thermonatrite, trona, pirssonite, calcite, borax and rarely tychite. At Borax Lake, California, USA, it is found with northupite and pirssonite.

Alteration

Gaylussite dehydrates with efflorescence in dry air. It alters readily to calcite. Calcite pseudomorphs after gaylussite have been described.

Gedrite

Formula: ☐Mg2(Mg3Al2)(Si6Al2)O22 (OH)2 inosilicate (chain silicate) amphibole
Specific gravity:
Hardness: 5½: to 6
Streak: White
Colour: Pale greenish-grey to brown
Environments:

Metamorphic environments

Gedrite occurs in contact and medium to high grade metamorphic rocks where it may be associated with garnet, cordierite, anthophyllite, cummingtonite, sapphirine, sillimanite, kyanite, quartz, staurolite or biotite.

Alteration

gedrite-ferro-gedrite and quartz to enstatite-ferrosilite, Fe-rich cordierite and H2O
(Mg,Fe2+)5Al4Si6O22(OH)2 + 2Si2 → 3(Mg,Fe2+)SiO3 + (Mg,Fe2+)2Al4Si5O18 + H2O
In the pyroxene-hornfels facies enstatite-ferrosilite may develop from gedrite-ferro-gedrite according to the above reaction.

Gehlenite

Formula: Ca2Al(SiAl)O7 sorosilicate (Si2O7 groups) melilite group
Specific gravity: 2.9 to 3.06
Hardness: 5 to 6
Streak: white, greyish white
Colour: colourless, greenish grey, yellowish brown
Solubility: Insoluble in water; soluble in hydrochloric acid forming an insoluble silica gel
Environments:

Metamorphic environments

Gehlenite is a contact metamorphic mineral in limestone. It is a mineral of the granulite facies.

Alteration

grossular to anorthite, gehlenite and wollastonite
2Ca3Al2(SiO4)3 ⇌ CaAl2Si2O8 + Ca2Al2SiO7 + 3CaSiO3
The equilibrium temperature for this reaction at 5 kbar pressure is 1,110oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

grossular and corundum to anorthite and gehlenite
2Ca3Al2(SiO4)3 + Al2O3 ⇌ CaAl2Si2O8 + Ca2Al2SiO7
The equilibrium temperature for this reaction at 5 kbar pressure is about 950oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

Common impurities: Ti,Fe,Mg,Mn,Na,K

Gibbsite

Formula:Al(OH)3 hydroxide
Specific gravity:
Hardness: 2½ to 3
Streak: White
Colour: White, light gray, light green, reddish white; reddish yellow (impure)
Solubility: Insoluble in water, hydrochloricand nitric acid; soluble in sulphuric acid

Plutonic igneous environments
Pegmatites
Sedimentary environments

Gibbsite is a secondary mineral forming in the weathered surface zones in clay deposits and limestone, as well as low-silica igneous rocks and pegmatites. It is a constituent of the aluminium ore bauxite.

Alteration

kaolinite and H2O to gibbsite and quartz
Al2Si2O5(OH)4 + H2O ⇌ 2Al(OH)3 + 2SiO2

Common impurities: Fe,Ga

Gilalite

Formula: Cu5Si6O17.7H2O
Tectosilicate (framework silicate) There are indications that a sharp loss of water occurs at about 92oC
Specific gravity: 2.82
Hardness: 2
Streak: Light green
Colour: Green to blue-green
Environments:

Metamorphic environments

Gilalite is a retrograde metamorphic or mesogene mineral formed at the expense of a prograde calc-silicate and sulphide assemblage, commonly encrusting fractures in garnet-diopside skarn. It is also found filling cracks or interstices in diopside grains. At the type locality, The Christmas mine, Arizona, USA, it is associated with kinoite, apachite, stringhamite, junitoite, clinohedrite, xonotlite, diopside, apophyllite, calcite and tobermorite.
Common impurities: Mn,Mg,Ca

Gismondine

Formula: Ca2(Si4Al4)O16.8H2O tectosilicate (framework silicate), zeolite group
Specific gravity: 2.12 to 2.28
Hardness: 4 to 5
Streak: White
Colour: Colourless, white, very pale pink
Environments:

Pegmatites
Sedimentary environments (tuff)
Metamorphic environments
Basaltic cavities

Gismondine is one of the rarer zeolites; it occurs most commonly in olivine basalt, less commonly in nepheline basalt, and tuff, schist or pegmatites.
In zeolite zones in basalt lavas it is associated with chabazite, thomsonite and phillipsite.

At Alexander dam, Hawaii, USA, gismondine has been reported in cavities associated with stilbite, allophane, olivine and augite.

Glauberite

Formula: Na2Ca(SO4)2 sulphate
Specific gravity: 2.7 to 2.8
Hardness: 2½ to 3
Streak: White
Colour: Grey, colourless, yellowish, red
Solubility: Soluble in water
Environments:

Sedimentary environments
Fumeroles

Glauberite occurs in dry salt-lake beds or marine evaporite deposits, generally in desert climates, and in fumeroles. Glauberite dissolves in water, depositing gypsum, so pseudomorphs of gypsum after glauberite are not uncommon.

Localities

Australia

At Lake Crosbie, Victoria, Australia, glauberite occurs associated with halite and gypsum in black mud under a salt crust which covers the lake.

USA

Camp Verde, Arizona, is known for pseudomorphs of calcite after glauberite.

Glaucochroite

Formula: CaMn2+(SiO4) nesosilicate (insular SiO4 groups) olivine group
Specific gravity:
Hardness: 6
Streak: White
Colour: Bluish-grey, pink, brown or white
Environments:

Metamorphic environments

Glaucochroite is found in metamorphosed limestone containing manganese minerals

Alteration

bustamite, tephroite and calcite to glaucochroite and CO2
CaMn2+Si2O6 + Mn2+2(SiO4) + 2CaCO3 ⇌ 3CaMn2+(SiO4) + 2CO2

Glaucophane

Formula: ☐Na2(Mg3Al2)Si8O22 (OH)2 inosilicate (chain silicate) amphibole
Specific gravity: 3.0 to 3.3
Hardness: 5½ - 6½
Streak: Light blue
Colour: Blue-grey, blue-lavender, blue-black
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments:

Metamorphic environments

Glaucophane is found only in metamorphic rocks such as schist, eclogite and marble. It is a low-temperature, relatively high pressure metamorphic mineral, occurring in association with jadeite, lawsonite and aragonite. It is a major constituent of glaucophane schist, and it is a characteristic mineral of the blueschist facies.

Alteration

albite, chlorite and calcite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz, CO2 and H2O
8Na(AlSi3O8) + (Mg4.0Fe2.0)(AlSi3O10)(OH)8 + CaCO3 → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 2SiO2 + CO2 + 2H2O
In low to intermediate metamorphism jadeite-glaucophane assemblages may arise from reactions such as the one above.

albite and montmorillonite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz and H2O
8Na(AlSi3O8) + 2Ca0.5(Mg3.5Al0.5)Si8O20(OH)4.nH2O → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 15SiO2 +6H2O
This reaction occurs in low to intermediate metatmorphism.

Common impurities: Li,Ti,Cr,Mn,Ca,K,F,Cl

Gmelinite

Gmelinite is the name for three minerals:
Gmelinite-Ca: Ca2(Si8Al4)O24.11H2O
Gmelinite-K: K4(Si8Al4)O24.11H2O
Gmelinite-Na4(Si8Al4)O24.11H2O
These minerals are tectosilicates (framework silicates), zeolite group
Specific gravity: 2.04 to 2.17
Hardness: 4½
Streak: White
Colour: Colourless, white, yellow, greenish white, orange, pale green, pink, red, brown and grey
Environments:

Pegmatites
Metamorphic environments
Hot spring deposits
Hydrothermal environments
Basaltic cavities

Gmelinite generally occurs in cavities in silica-poor volcanic rocks, and also in sodium-rich pegmatites and 55 to 75oC geothermal wells. No sedimentary gmelinite has been reported. It is a product of diagenetic reactions, hydrothermal activity or alteration of basalt. Common associates are other zeolites, quartz, aragonite and calcite.

In the zeolite localities of Northern Ireland gmelinite is associated with chabazite, thomsonite, analcime, phillipsite, lévyne, calcite and aragonite.

Goethite

Formula: FeO(OH) oxide containing hydroxyl
Specific gravity: 4.3
Hardness: 5 to 5½
Streak: Brown to brownish yellow
Colour: Yellow, brown to dark brown and reddish brown
Solubility: Slightly soluble in hydrochloric acid
Environments:

Pegmatites
Carbonatites
Sedimentary environments
Hydrothermal environments

Goethite is a very common mineral, typically formed by the oxidation of iron-bearing minerals. It also forms as a direct inorganic or biogenic precipitate from water and it is widespread as a deposit in bogs and springs. Large quantities of goethite have resulted from the weathering of serpentine. It also occurs in vesicles in volcanic rocks, and in the oxidation zone of hypothermal (high temperature) hydrothermal veins.

Alteration

hematite and H2O to goethite
Fe2O3 + H2O ⇌ 2FeO(OH)
Both forward and reverse reactions are slow, but equilibrium in most natural environments is displaced to the left, favouring the formation of hematite.

Common impurities: Mn

Gold

Formula: Au native element
Specific gravity: 15.5 - 19.3
Hardness: 2½ to 3
Streak: Shining yellow
Colour: Shining yellow
Solubility: Insoluble in hydrochloric, sulphuric and nitric acids
Melting Point: 1062.4° ± 0.8°
Environments:

Plutonic igneous environments
Placer deposits (typical)
Hydrothermal environments (typical)

Gold is a rare element that is widely distributed but in small amounts. Most gold occurs as the native metal. The chief sources of gold are hypothermal (high temperature) mesothermal (moderate temperature) and epithermal (low temperature) hydrothermal gold-quartz veins, together with pyrite and other sulphides. When gold-bearing veins are weathered, the gold liberated either remains in place in the soil mantle, or is washed into neighbouring streams to form placer deposits.

Alteration

Gold is usually primary, but it can also occur as a secondary mineral derived from gold tellurides.
Pseudomorphs of gold after pyrite are extremely rare, but examples so well formed that they seem artificial are found at the Lena goldfields, Bodaibo Area, Eastern Siberia, Russia.
Common impurities: Ag,Cu,Pd,Hg

Gonnardite

Formula: (Na,Ca)2(Si,Al)5O10.3H2O tectosilicate (framework silicate), zeolite group
Specific gravity: 2.21 to 2.36
Hardness: 4½ to 5
Streak: White
Colour: Colourless, white, yellow, pink to salmon-orange
Environments:

Volcanic Igneous environments
Pegmatites
Metamorphic environments (rarely)

Gonnardite occurs in silica-poor volcanic rocks and pegmatites, and rarely in skarn. Crystals are often found with cores of gonnardite and rims of thomsonite.

Alteration

Gonnardite forms overgrowths on natrolite.

Gordonite

Formula: MgAl2(PO4)2(OH)2.8H2O hydrated phosphate with hydroxyl
Specific gravity: 2.319
Hardness: 3½
Streak: White
Colour: Smoky-white, buff, colourless; crystals = pale pink or pale green on tips, colourless in transmitted light
Solubility: Soluble in acids

Environments:

Pegmatites
Hydrothermal environments

Gordonite is a rare secondary mineral formed from the alteration of variscite in nodules in limestone or as a late-stage hydrothermal mineral in complex granitic pegmatites.

Gossan

Gossan is an iron-bearing weathered product overlying a sulphide deposit, formed by the oxidation of sulphides and the leaching-out of the sulphur and most metals, leaving mainly hydrated iron oxides.

Graphite

Formula: C native element
Specific gravity: 2.09 to 2.23
Hardness: 1 to 2
Streak: Black to steel-grey
Colour: Black to steel-grey
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Pegmatites
Metamorphic environments (typical)
Hydrothermal environments

Graphite most commonly occurs in metamorphic environments, where it may form a considerable proportion of the rock. In these cases, it has probably been derived from carbonaceous material of organic origin that has been converted into graphite during metamorphism. It can also be found in veins and in pegmatites.
It is a mineral of the greenschist, amphibolite and granulite facies.
Graphite is a common constituent of phyllite, and it also may be found in limestone, schist and gneiss.
Graphite is the low pressure, high temperature polymorph of diamond. At 200oC graphite is the stable polymorph at pressures up to about 20 kbar.

Greenalite

Formula: (Fe2+, Fe3+2-3Si2O5(OH)4 phyllosilicate (sheet silicate) serpentine group
Specific gravity: 2.85 to 3.15
Hardness: 2½
Streak: Greenish grey
Colour: Green, light yellow-green
Environments:

Sedimentary environments

Greenalite is a primary phase in some banded iron formations

Alteration

Mg-rich greenalite to olivine, Mg-rich grunerite and H2O
18(Fe2+, Mg))3Si2O5(OH)4 → 20(Fe,Mg)2SiO4 + 2(Fe2+,Mg)7Si8O22(OH)2 + 34H2O

Mg-rich greenalite to olivine, SiO2 and H2O
2(Fe2+, Mg))3Si2O5(OH)4 → 3(Fe,Mg)2SiO4 + SiO2 + 4H2O

Common impurities: Al,Mn,Mg

Grossular

Formula: Ca3Al2(SiO4)3 nesosilicate (insular SiO4 groups), garnet group
Specific gravity: 3.594
Hardness: 6½ to 7
Streak: White to pale brownish white
Colour: Brown, orange, red, yellow, green, white, colourless. colourless when pure (rare), commonly red orange to brown.
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Metamorphic environments

Grossular occurs in contact and regionally metamorphosed limestone; it is a mineral of the hornblende-hornfels, pyroxene-hornfels, amphibolite and granulite facies.

Alteration

calcium amphibole, grossular and quartz to diopside- hedenbergite, anorthite, pyrope-almandine and H2O
2Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + Ca3Al2(SiO4)3 + SiO2 = 3Ca(Fe,Mg)Si2O6 + 4Ca(Al2Si2O8) + (Mg,Fe2+)3Al2(SiO4)3 + 2H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

anorthite to grossular, kyanite and quartz
3CaAl2 Si2O8 → Ca3Al2(SiO4)3 + 2Al2OSiO4 + SiO2
At 20 kbar pressure the equilibrium temperature is about 1,000oC and at 30 kbar it is about 1,400oC

epidote and quartz to anorthite, grossular and H2O
4Ca2Al3(SiO4)3(OH) + SiO2 → 5CaAl2Si2O8 + Ca3Al2(SiO4)3 + 2H2O
This reaction occurs as the degree of metamorphism increases

grossular to anorthite, gehlenite and wollastonite
2Ca3Al2(SiO4)3 ⇌ CaAl2Si2O8 + Ca2Al2SiO7 + 3CaSiO3
The equilibrium temperature for this reaction at 5 kbar pressure is 1,110oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

grossular and corundum to anorthite and gehlenite
2Ca3Al2(SiO4)3 + Al2O3 ⇌ CaAl2Si2O8 + Ca2Al2SiO7
The equilibrium temperature for this reaction at 5 kbar pressure is about 950oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

grossular, diopside, monticellite, calcite and H2O to vesuvianite, quartz and CO2
10Ca3Al2(SiO4)3 + 3CaMgSi2O6 + 3CaMg(SiO4) + 2CaCO3 + 8H2O ⇌ 2Ca19Al10Mg3(SiO4)10 (Si2O2)4O2(OH)8 + 3SiO2 + 2CO2
A common association in calc-silicate metamorphism can be represented by the above equation. Vesuvianite stability will tend to increase with increasing water and decrease as the activity of CO2 rises.

grossular and kyanite to anorthite and corundum
Ca3Al2(SiO4)3 + 3Al2OSiO4 ⇌ 3CaAl2Si2O8 + Al2O3
The equilibrium temperature for this reaction at 10 kbar pressure is about 540oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

grossular kyanite and quartz to anorthite
Ca3Al2(SiO4)3 + 2Al2OSiO4 + SiO2 ⇌ 3CaAl2Si2O8
The equilibrium temperature for this reaction at 10 kbar pressure is about 510o (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

grossular and quartz to anorthite and wollastonite
Ca3Al2(SiO4)3 + SiO2 ⇌ CaAl2Si2O8 + 2CaSiO3
The equilibrium temperature for this reaction at 5 kbar pressure is 730oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

hornblende, grossular and quartz to Fe-rich diopside, anorthite, almandine and H2O
2Ca2(Mg,Fe2+)3(Al4Si6)O22(OH)2 + Ca3Al2Si3O12 + 2SiO2 = 3Ca(Mg,Fe2+)Si2O6 + 4CaAl2Si2O8 + (Mg,Fe2+)Al2Si3O12 + 2H2O
Fe-rich diopside occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies. The above reaction is typical.

meionite (scapolite series), calcite and quartz to grossular and CO2
Ca4Al6O24(CO3) + 5CaCO3 + 3SiO2 ⇌ 3Ca3Al2(SiO4)3 + 6CO2

zoisite to anorthite, grossular, corundum and H2O
6Ca2Al3[Si2O7][SiO4]O(OH) ⇌ 6CaAl2Si2O8 + 2Ca3Al2Si3O12 + Al2O3 + 3H2O
The equilibrium temperature for this reaction at 6 kbar pressure is about 760oC, and at 10 kbar it is about 950oC (granulite facies). For any given pressure, the reaction goes to the right at higher temperatures, and to the left at lower temperatures.

zoisite and quartz to grossular, anorthite and H2O
4Ca2Al3[Si2O7][SiO4]O(OH) + SiO2 ⇌ Ca3Al2Si3O12 + 5CaAl2Si2O8 + 2H2O
The equilibrium temperature for this reaction at 5 kbar pressure is 650oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

Common impurities: Fe,Cr

Grunerite

Formula: ☐Fe2+2Fe2+5Si8O22(OH)2 inosilicate (chain silicate) amphibole
Specific gravity: 3.4 to 3.5
Hardness: 5 to 6
Streak: Colourless
Colour: Ashen, brown, brownish green, dark gray
Environments:

Metamorphic environments

Grunerite is common in iron formations due to medium to high grade contact metamorphism, and it also occurs in some blueschist facies quartzite.
Upon further metamorphism cummingtonite and grunerite give way to orthopyroxene or olivine.

Alteration

cummingtonite-grunerite and H2O to serpentine and quartz
6(Fe,Mg)7Si8O22(OH)2 + 22H2O ⇌ 7(Fe,Mg)6Si4O10(OH)8 + 20SiO2

cummingtonite-grunerite and olivine to enstatite-ferrosilite and H2O
(Fe,Mg)7Si8O22(OH)2 + (Mg,Fe)2SiO4 ⇌ 9(Mg,Fe2+)SiO3 + H2O

enstatite-ferrosilite, SiO2 and H2O to cummingtonite-grunerite
7(Mg,Fe2+)SiO3 + SiO2 + H2O ⇌ (Fe,Mg)7Si8O22(OH)2

fayalite, SiO2 and H2O to grunerite
7Fe2+2(SiO4) + 9SiO2 + 2H2O → 2Fe2+2Fe2+5Si8O22(OH)2 Fayalite may undergo partial regression to grunerite according to the above reaction.

ferro-actinolite to hedenbergite, grunerite, quartz and H2O
7Ca2Fe2+5Si8O22(OH)2 → 14CaFe2+Si2O6 + 3Fe2+2Fe2+5 Si8O22(OH)2 + 4SiO2 + 4H2O
In some calc-silicate rocks hedenbergite is the product of metamorphism of iron-rich sediments, probably due to the instability of ferro-actinolite with rising temperature. The association of hedenbergite and grunerite has been widely described, and its formation may be due to the above reaction.

Mg-rich greenalite to olivine, Mg-rich grunerite and H2O
18(Fe2+, Mg))3Si2O5(OH)4 → 20(Fe,Mg)2SiO4 + 2(Fe2+,Mg)7Si8O22(OH)2 + 34H2O

Gypsum

Formula: Ca(SO4).2H2O sulphate
Specific gravity: 2.3 to 2.4
Hardness: 1½ to 2
Streak: White
Colour: Colourless, white, yellowish, pink
Solubility: Moderately soluble in hydrochloric acid
Environments:

Sedimentary environments
Fumeroles
Hydrothermal environments

Gypsum is the commonest of the sulphate minerals, found in chemical sedimentary environments, where it frequently occurs interstratified with limestone and shale. It is usually found as a layer underlying beds of rock salt, having been deposited there as one of the first minerals to crystallise on the evaporation of salt waters. It may recrystallise in veins forming satin spar. It is also common as a gangue mineral in metallic veins, at fumaroles, and in the oxidation zones of sulphide deposits. Gypsum is also found in volcanic regions, especially where limestone has been acted on by sulphur vapours.
Gypsum is associated with many different minerals, the more common being halite, anhydrite, dolomite, calcite, sulphur, pyrite and quartz.

Alteration

Glauberite dissolves in water, depositing gypsum, so pseudomorphs of gypsum after glauberite are not uncommon.

anhydrite and water to gypsum
Ca(SO4) + 2H2O ⇌ Ca(SO4).2H2O
Gypsum is frequently formed by the hydration of anhydrite.

anorthite, H2SO4 and H2 to gypsum and kaolinite
CaAl2 Si2O8 + H2SO4 + 3H2O → CaSO4.2H2O + Al2Si2O5(OH)4

Localities

Australia

At Lake Crosbie, Victoria, Australia, gypsum occurs associated with halite and glauberite in black mud under a salt crust which covers the lake.

Gyrolite

Formula: NaCa16(Si23Al)O60(OH)8.14H2O phyllosilicate Formula:
Specific Gravity: 2.36 to 2.45
Hardness: 3 to 4
Streak: White
Colour: Brown, colourless, white, green
Solubility: Decomposed by acids
Environments:

Basaltic cavities

Gyrolite is a secondary mineral that occurs in amygdules in basalt. It is stable under saturated steam conditions from 120 to 200oC.
Common impurities: Fe, Mg

Halite

Formula: NaCl chloride
Specific gravity: 2.1 to 2.2
Hardness: 2
Streak: White
Colour: Colourless, white, redish, yellow, grey, blue
Solubility: Readily soluble in water
Melts at 804°.
Environments:

Sedimentary environments
Fumeroles and hot spring deposits

Halite is dissolved in the waters of salt springs, salt lakes and the ocean. It is a common mineral, occurring often in extensive beds and irregular masses, precipated by evaporation with gypsum, sylvite, anhydrite and calcite. It is a major salt in playa deposits of enclosed basins. It occurs as halite deposits in steppes and deserts, and in fumeroles.

Common impurities: I,Br,Fe,O

Localities

Australia

At Lake Crosbie, Victoria, Australia, halite occurs associated with glauberite and gypsum in black mud under a salt crust which covers the lake.

Halloysite

Formula: Al2Si2O5(OH)4.2H2O phyllosilicate (sheet silicate)
Specific gravity: 2.0 to 2.65
Hardness: 1 to 2
Streak: Paler than the color, or white.
Colour: White to tan, sometimes greenish or bluish, also chocolate brown to reddish. br Environments:

Plutonic igneous environments
Volcanic igneous environments
Pegmatites rarely
Hot spring deposits

Halloysite is a product of hydrothermal alteration or surface weathering of aluminosilicate minerals such as feldspar. Ongoing formation is observed at hot springs. It is frequently found as an alteration of basaltic rocks or in hydrothermally altered fissures in monzonite. It also may be derived from chlorite, mica, rhyolite, granite, volcanic ash, tuff and volcanic glass. It is found rarely in granite pegmatites and bauxite and clay. Commonly associated with kaolinite, illite, minerals of the smectite group (which includes montmorillonite and nontronite), allophane.

Alteration

Halloysite easily weathers to kaolinite, but can also be derived from it. It is sometimes associated with allophane and may be derived from it.

Common impurities: Ti,Ca,Na,K,Fe,Cr,Mg,Ni,Cu

Hanksite

Formula: KNa22(SO4)9(CO3)2Cl anhydrous compound sulphate containing halide
Specific gravity: 2.562
Hardness: 3 to 3½
Streak: White
Colour: Colourless to grey, yellow or almost black; colourless in transmitted light
Solubility: Readily soluble in water, effervesces weakly in dilute acids
Environments:

Sedimentary environments

Hanksite occurs in lacustrine (lake) evaporite deposits. It is abundant at Searles Lake, California, USA, associated with halite, borax, trona and aphthitalite.

Harmotome

Formula: Ba2(Si12Al4)O32.12H2O tectosilicate (framework silicate), zeolite group
Specific gravity: 2.41 to 2.47
Hardness: 4 to 5
Streak: White
Colour: Colorless, white, grey, pink, yellow, brown

Sedimentary environments (rarely)
Metamorphic environments
Basaltic cavities

Harmotome occurs in basaltic cavities associated with calcite and rarely natrolite. It has also been reported in tuff associated with calcite, laumontite and pyrite.

At Nisikkatch lake, Saskatchewan, Canada, harmotome occurs in veins in gneiss associated with hyalophane (variety of microcline) and albite.

In northern Italy harmotome occurs in graphite lenses in gneiss with quartz, sphalerite and galena.

In the Ural mountains, Russia, harmotome occurs in bauxite with kaolinite and halloysite.

At the Struy lead mines, Inverness, Scotland, UK, harmotome occurs in hydrothermal veins with sphalerite, baryte and calcite.

Common impurities: Na,Ca

Hausmannite

Formula: Mn2+Mn3+2O4, multiple oxide with a distorted spinel structure, although it is not a member of the spinel group
Specific gravity: 4.83 to 4.85
Hardness: 5½
Streak: Dark reddish brown, dark brown
Colour: Brown-black
Solubility: Soluble in hot hydrochloric acid with the evolution of Cl2.
Epitaxy: Hausmannite and jacobsite have been found as oriented intergrowths.
Environments:

Metamorphic environments
Hydrothermal environments

Hausmannite is a primary mineral in hydrothermal veins. It may also be produced by metamorphism of manganiferous rocks. At the type locality, Thuringia, Germany, it occurs in a manganese ore deposit.
At the Woods mine, New South Wales, Australia, hausmannite forms by oxidation and loss of SiO2 from neotocite and tephroite.

Alteration

braunite to hausmannite, SiO2 and O2
3Mn2+Mn3+6O8(SiO4) ⇌ 7Mn2+Mn3+2O4 +3SiO2 + O2

braunite to hausmannite, rhodonite and O2
2Mn2+Mn3+6O8(SiO4) ⇌ 4Mn2+Mn3+2O4 + 2Mn2+SiO3 + O2
A higher temperature favours the forward reaction

braunite to tephroite, hausmannite and O2
3Mn2+Mn3+6O8(SiO4) ⇌ 3Mn2+2(SiO4) + 5Mn2+Mn3+2O4 + 2O2

hausmannite and O2 to bixbyite
4Mn2+Mn3+2O4 + O2 ⇌ 6Mn2O3

hausmannite and quartz to rhodonite and O2
2Mn2+Mn3+2O4 + 6SiO2 ⇌ 6Mn2+SiO3 + O2

hausmannite and rhodonite to tephroite and O2
2Mn2+Mn3+2O4 + 6Mn2+SiO3 ⇌ 6Mn2+2SiO4 + O2

manganosite and O2 to hausmannite
6MnO + O2 ⇌ 2Mn2+Mn3+2O4
A higher temperature favours the reverse reaction

rhodochrosite and O2 to hausmannite and CO2
6MnCO3 + O2 ⇌ 2Mn2+Mn3+2O4 +6CO2

Common impurities: Zn,Fe,Ca,Ba,Mg

Hedenbergite

Formula: CaFe2+Si2O6 inosilicate (chain silicate) pyroxene group
Specific gravity: 3.5 to 3.6
Hardness: 5 - 6
Streak: Greenish, brownish, grey, also colourless
Colour: Dark green, greenish black, brownish black, black
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Plutonic igneous environments
Metamorphic environments

Hedenbergite is common in iron-rich metamorphic rocks, such as skarn, in alkaline granite and as xenoliths in kimberlite.

Alteration

aenigmatite, anorthite and O2 to hedenbergite, albite, ilmenite and magnetite
½Na4[Fe2+10Ti2]O4[Si12O36] + CaAl2Si2O8 + ½O2 = CaFe2+Si2O6 + 2NaAlSi3O8 + Fe2+Ti4+O3 + Fe2+Fe3+2O4

ankerite-dolomite and quartz to diopside-hedenbergite and CO2
Ca(Fe,Mg)(CO3)2 + 2SiO2 = Ca(Fe,Mg)Si2O6 + 2CO2

calcium amphibole, calcite and quartz to diopside-hedenbergite, anorthite, CO2 and H2O
Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + 3CaCO3 + 4SiO2 = 3Ca(Fe,Mg)Si2O6 + 2Ca(Al2Si2O8) + 3CO2 + H2O Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

calcium amphibole, grossular and quartz to diopside- hedenbergite, anorthite, pyrope-almandine and H2O
2Ca2(Mg,Fe2+)3Al4Si6O22(OH)2 + Ca3Al2(SiO4)3 + SiO2 = 3Ca(Fe,Mg)Si2O6 + 4Ca(Al2Si2O8) + (Mg,Fe2+)3Al2(SiO4)3 + 2H2O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction.

Fe-rich cordierite and diopside- hedenbergite to enstatite- ferrosilite, anorthite and quartz
(Mg,Fe)2 Al4Si5O18 + 2Ca(Mg,Fe)Si2O6 = 4(Mg,Fe2+)SiO3 + 2Ca(Al2Si2O8) + SiO2

diopside-hedenbergite and CO2 to enstatite-ferrosilite, calcite and quartz
Ca(Mg,Fe)Si2O6 + CO2 → (Mg,Fe2+)SiO3 + CaCO3 + SiO2

enstatite-ferrosilite, diopside-hedenbergite, albite, anorthite and H2O to amphibole and quartz
3(Mg,Fe2+)SiO3 + Ca(Mg,Fe2+)Si2O6 + NaAlSi3O8 + Ca(Al2Si2O8) + H2O ⇌ NaCa2(Mg,Fe)4Al(Al2O6)O22(OH)2 + 4SiO2 This reaction represents metamorphic reactions between the granulite and amphibolite facies.

ferro-actinolite to hedenbergite, grunerite, quartz and H2O
7Ca2Fe2+5Si8O22(OH)2 → 14CaFe2+Si2O6 + 3Fe2+2Fe2+5 Si8O22(OH)2 + 4SiO2 + 4H2O
In some calc-silicate rocks hedenbergite is the product of metamorphism of iron-rich sediments, probably due to the instability of ferro-actinolite with rising temperature. The association of hedenbergite and grunerite has been widely described, and its formation may be due to the above reaction.

ferro-actinolite, calcite and quartz to hedenbergite, CO2 and H2O
Ca2Fe2+5Si8O22(OH)2 + 3CaCO3 + 2SiO2 ⇌ 5CaFe2+Si2O6 + 3CO2 + H2O In some calc-silicate rocks hedenbergite is the product of metamorphism of iron-rich sediments, according to the above reaction, probably due to the instability of ferro-actinolite with rising temperature.

hematite, wüstite, quartz and calcite to andradite, hedenbergite and magnetite
2Fe2O3 + 2FeO + 5SiO2 + 4CaCO3 → Ca3Fe3+2(SiO4)3 + CaFe2+Si2O6 +Fe2+Fe3+2O4 +4CO2

titanomagnetite (ilmenite combined with magnetite), quartz, and aegirine-hedenbergite to aenigmatite, hedenbergite, magnetite and O2
6(Fe2+Ti4+O3 + Fe2+Fe3+2O4) + 12SiO2 + 12(NaFe3+Si2O6 + CaFe2+Si2O6) ⇌ 3Na4[Fe2+10Ti2]O4[Si12O36] + 12CaFe2+Si2O6 + 2Fe2+Fe3+2O4 + 5O2

Common impurities: Mn,Zn,Ti,Al,Mg,Na,K

Hedyphane

Formula: Ca2Pb3(AsO4)3Cl
Anhydrous phosphate containing halogen, hedyphane group, apatite supergroup
Specific gravity: 5.82
Hardness: 4½
Streak: White
Colour: White, yellow-white, bluish
Solubility: Soluble in nitric acid
Environments:

Metamorphic environments
Hydrothermal environments

Hedyphane is a relatively rare secondary mineral found in metamorphosed manganese deposits.

At Långban, Värmland, Sweden (the type locality), hedyphane occurs filling fissures in a garnet-pyroxene matrix, associated with baryte, barylite, rhodonite, hausmannite, bixbyite, phlogopite, amphibole and calcite. Specimens have been found consisting of massive, calcite-bearing rock, coated with calcite crystals. These are, in turn, coated with hedyphane crystals, followed by sparse amounts of allactite and two generations of hausmannite.

At Pajsberg, Värmland, Sweden, hedyphane occurs with tephroite and calcite in magnetite.

At Franklin, New Jersey, USA, hedyphane is the most abundant non-silicate lead mineral, associated with barylite, calcite, willemite, native copper, native lead, hancockite, rhodonite, baryte, manganaxinite, apatite and cahnite in veinlets in a metamorphosed zinc orebody. In some specimens hedyphane is the chief mineral, forming the matrix for the other species; in others calcite encloses the other minerals. Specimens of hedyphane from the Parker Shaft, Franklin mine, contain hedyphane associated with axinite, grossular and hancockite.

Hematite

Formula: Fe2O3 oxide
Specific gravity: 5.2 to 5.3
Hardness: 6½
Streak: Reddish brown
Colour: Reddish brown, grey, black
Solubility: Slightly soluble in hydrochloric acid
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites
Sedimentary environments
Metamorphic environments (typical)
Volcanic sublimates and hot spring deposits
Hydrothermal environments

Hematite occurs as microscopic grains in almost all rocks, especially metamorphic rocks.
It is found in plutonic igneous environments as an accessory mineral in feldspar-rich igneous rocks such as granite, and in pegmatites and carbonatites.
Large ore bodies of hematite are usually of sedimentary origin. Hematite is also found in red sandstone as the cementing material that binds the quartz grains together.
Hematite occurs both in contact and regional metamorphic deposits, where it may have originated from the oxidation of limonite, siderite or magnetite.
It occurs in disseminated hydrothermal replacement deposits and in hydrothermal replacement lodes, as well as in the oxidation zone of epithermal (low temperature) and mesothermal (moderate temperature) hydrothermal veins.
It may also occur as a sublimation due to volcanic activity.

Hematite is a common constituent of marl.

Alteration

Hematite may form as an alteration product of ilmenite.

aegirine, epidote and CO2 to albite, hematite, quartz, calcite and H2O
4NaFe3+Si2O6 + 2Ca2(Al2Fe3+ [Si2O7](SiO4)O(OH) + 4CO2 → 4Na(AlSi3O8) + 3Fe2O3 + 2SiO2 + 4CaCO3 + H2O

calcite, hematite and quartz to andradite and CO2
3CaCO3 + Fe2O3 + 3SiO2 → Ca3Fe3+2Si3O12 + 3CO2

fayalite, oxygen and H2O to hematite and silicic acid
2Fe2SiO4 + O2 + 4H2O → 2Fe2O3 + 2H4SiO4
On prolonged exposure to the air Fe2+ compounds are oxidised to Fe3+ compounds according to reactions such as the one above.

hematite and H2O to goethite
Fe2O3 + H2O ⇌ 2FeO(OH)
Both forward and reverse reactions are slow, but equilibrium in most natural environments is displaced to the left, favouring the formation of hematite.

hematite, wüstite, quartz and calcite to andradite, hedenbergite, magnetite and CO2
2Fe2O3 + 2FeO + 5SiO2 + 4CaCO3 → Ca3Fe3+2(SiO4)3 + CaFe2+Si2O6 +Fe2+Fe3+2O4 +4CO2

magnetite to hematite
2Fe3O4 + ½O2 ⇌ 3Fe2O3
Equilibrium is to one side or the other depending on temperature and pressure.

siderite, oxygen and H2O to hematite and silicic acid
2Fe2CO3 + O2 + 4H2O → 2Fe2O3 + 2H2CO3
On prolonged exposure to the air Fe2+ compounds are oxidised to Fe3+ compounds according to reactions such as the one above.

Common impurities: Ti,Al,Mn,H2O

Hemimorphite

Formula: Zn4(Si2O7)(OH)2.H2O sorosilicate (Si2O7 groups)
Specific gravity: 3.475
Hardness: 4½ to 5
Streak: White
Colour: colourless, white, pale blue, pale green, gray, brown
Solubility: Slightly soluble in hydrochloric acid
Environments:

Hydrothermal environments

Hemimorphite is a high temperature secondary mineral found in the oxidation portion of zinc deposits, associated with smithsonite, sphalerite, cerussite, anglesite and galena.
In the oxidation zone of epithermal veins sphalerite ZnS (primary) alters to secondary hemimorphite Zn4Si2O7(OH)2.H2O, smithsonite ZnCO3 and manganese-bearing willemite Zn2SiO4.

Common impurities: Cu,Fe

Hercynite

Formula: Fe2+Al2O4 multiple oxide, spinel group
Specific gravity: 3.95
Hardness: 7½
Streak: Dark greyish green to dark green
Colour: Dark blue-green, yellow, brown, black
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments:

Plutonic igneous environments
Placer deposits
Metamorphic environments

Hercynite occurs in high grade metamorphosed ferruginous argillaceous sediments and in some mafic and ultramafic igneous rocks. Also in placers.

Alteration

enstatite-ferrosilite and andalusite to Fe-rich cordierite and spinel-hercynite
5(Mg,Fe2+)SiO3 + 5 Al2SiO5 → 2(Mg,Fe2+)2Al4Si5O18 + (Mg,Fe2+)Al2O4
In medium-grade thermally metamorphosed argillaceous rocks originally rich in chlorite and with a low calcium content, the association of andalusite with enstatite-ferrosilite is excluded by the above reaction.

spinel-hercynite, sillimanite and quartz to sapphirine
7(Mg,Fe2+)Al2O4 + 2Al2SiO5 + SiO2 → 4(Mg,Fe)1.75Al4.5Si0.75O10

staurolite, annite and O2 to hercynite, magnetite, muscovite,corundum, SiO2 and H2O
2Fe2+2Al9Si4O23(OH) + KFe2+3 (AlSi3O10)(OH)2 +2O2 → 4Fe2+Al2O4 + Fe2+Fe3+2O4 + KAl2 (AlSi3O10)OH)2 + 4Al2O3 + 8SiO2 + 2H2O

Heulandite

The heulandite group is a group of tectosilicates (framework silicates) and a sub-group of the zeolite group, comprising:

heulandite-Ba (Ba,Ca,K)5(Si27Al9)O72.22H2O,
heulandite-Ca (Ca,Na,K)5(Si27Al9)O72.26H2O,
heulandite-K (K,Ca,Na)5(Si27Al9)O72.26H2O,
heulandite-Na (Na,Ca,K)5(Si27Al9)O72.22H2O
heulandite-Sr (Sr,Ca,Na)5(Si27Al9)O72.24H2O
Specific gravity: 2.2
Hardness: 3½ to 4
Streak: White
Colour: Colourless, white, yellowish, red
Solubility: Moderately soluble in hydrochloric acid
Environments:

Pegmatites
Basaltic cavities

Heulandite is usually found in cavities of mafic igneous rocks associated with zeolites and calcite. It also occurs as druses in pegmatites.
It is found associated with stilbite and pyrite in water tunnels under Queens, New York City, USA, and with stilbite, datolite and chabazite at the Quarry Road Cut, also New York City.
It occurs on weathering scapolite in the Carlin trench, The Selleck Road Tremolite and Tourmaline Locality, West Pierrepont, St. Lawrence County, New York.
At Palabora, Limpopo Province, South Africa it has been reported in association with calcite, saponite, and fluorapophyllite.
Geothermal wells have been drilled through a thick series of basalt flows in western Iceland, where it was found that heulandite crystallised at temperatures from 65oC to 200oC at depths between 30m and 1200m.

Hidalgoite

Formula: PbAl3(AsO4)(SO4)(OH)6
Specific gravity: 3.71 to 3.96
Hardness: 4½
Streak: White
Colour: White
Solubility: Insoluble in hydrochloric, nitric and sulphuric acid.

Hydrothermal environments

Hidalgoite is a secondary mineral in the oxidised zone of polymetallic sulphide deposits. At the type locality, the San Pascual Mine, Mexico, it occurs in an oxidised ore vein, associated with beudantite, tourmaline, limonite, mansfieldite and carbonate-cyanotrichite.

Holdenite

Formula: Mn2+6Zn3(AsO4)2(SiO4)(OH)8
Compound arsenate
Specific gravity: 4.11
Hardness: 4
Streak: White
Colour: Pink to deep red
Environments:

Hydrothermal environments

At the type locality, Franklin, New Jersey, USA, holdenite is a secondary mineral in veinlets, on slip surfaces and as interstitial̄ fillings within a metamorphosed stratiform zinc deposit associated with franklinite, willemite, pyrochroite, baryte, kolicite, sussexite, kraisslite, zincite, sphalerite, galena, calcite and rhodochrosite.

Hollandite

Formula: Ba(Mn4+6Mn3+2)O16
cryptomelane group
Specific gravity: 4.95
Hardness: 6
Streak: Black
Colour: Slivery grey to black
Environments:

Metamorphic environments
Hydrothermal environments

Hollandite is a primary mineral in contact metamorphic manganese ores, and a secondary weathering product of earlier manganese-bearing minerals, associated with bixbyite, braunite piemontite and other manganese oxides.
At Ilfeld, Harz mountains, Germany, hollandite occurs rarely in fissures in massive manganite ores, or encrusting baryte.
At Kajlidongri, Jhabua state, India, hollandite occurs in quartz veins traversing a manganese orebody.
At Nuba Mountain, Kordofan Province, Sudan, hollandite occurs intergrown with pyrolusite.

Common impurities: Fe,Pb,K,Na

Hornblende

Hornblende is a series between ferro-hornblende: ☐Ca2(Fe2+4Al) (Si7Al)O22(OH)2 and Magnesio-hornblende: ☐Ca2(Mg4Al) (Si7Al)O22(OH)2
Both are inosilicates (chain silicates) amphiboles
Specific gravity: 3.00 to 3.47
Hardness: 5 to 6
Streak: White
Colour: Green, black, brown
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Plutonic igneous environments
Volcanic igneous environments
Pegmatites
Metamorphic environments

Hornblende is an important and widely distributed primary, rock-forming mineral, occurring both in igneous and in metamorphic rocks; it is particularly characteristic of amphibolite in which hornblende and associated plagioclase feldspar are the major constituents.
In metamorphic environments hornblende is found both in contact and in regional metamorphic environments.
Hornblende is an essential constituent of ultramafic rocks
It is a common constituent of granite, syenite, diorite and gabbro.
It also may be found in trachyte, andesite, basalt and gneiss.
Hornblende is characteristic of the hornblende-hornfels and amphibolite facies, and it is also a mineral of the greenschist, granulite, blueschist and albite-epidote-hornfels facies.

Alteration

Hornblende characteristically alters from pyroxene both during the late stages of crystallisation of igneous rocks and during metamorphism.

anorthite, enstatite, spinel, K2O and H2O to Al-rich hornblende, Mg-rich sapphirine and phlogopite
2.5Ca(Al2Si2O8) + 10MgSiO3 + 6MgAl2O4 + K2O + 3H2O → Ca2.5Mg4Al(Al2Si6)O22(OH)2 + 3Mg2Al4SiO10 + 2KMg3(AlSi3O10)(OH)2
This reaction occurs in the granulite to amphibolite facies.

epidote and chlorite to hornblende and anorthite
6Ca2Al3(SiO4)3(OH) + Mg5Al2Si3O18(OH)8 → Ca2Mg5Si8O22(OH)2 + 10CaAl2Si2O8
This reaction represents changes when the metamorphic grade increases from the greenschist facies to the amphibolite facies.

hornblende, calcite and quartz to Fe-rich diopside, anorthite, CO2 and H2O
Ca2(Mg,Fe2+)3(Al4Si6)O22(OH)2 + 3CaCO3 + 4SiO2 = 3Ca(Mg,Fe2+)Si2O6 + 2Ca(Al2Si2O8) + 3CO2 + H2O
Fe-rich diopside occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies. The above reaction is typical.

hornblende, grossular and quartz to Fe-rich diopside, anorthite, almandine and H2O
2Ca2(Mg,Fe2+)3(Al4Si6)O22(OH)2 + Ca3Al2Si3O12 + 2SiO2 = 3Ca(Mg,Fe2+)Si2O6 + 4CaAl2Si2O8 + (Mg,Fe2+)Al2Si3O12 + 2H2O
Fe-rich diopside occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies. The above reaction is typical.

Al-rich hornblende, spinel, quartz, K2O and H2O to anorthite, Mg-rich sapphirine and phlogopite
Ca2.5Mg4Al(Al2Si6)O22(OH)2 + 4 MgAl2O4 + 6SiO2 + K2O + H2O → 2.5Ca(Al2Si2O8) + Mg2Al4SiO10 + 2KMg3(AlSi3O10)(OH)2

spinel and tremolite to forsterite and magnesio-hornblende
MgAl2O4 + Ca2Mg5Si8O22(OH)2 ⇌ Mg2SiO4 + Ca2(Mg4Al)(Si7Al)O22(OH)2
This reaction occurs in some strongly metamorphosed serpentinite.

Common impurities: Ti,Mn,Na,K

Hübnerite

Formula: Mn2+(WO4) anhydrous tungstate, but according to Mindat this species is misclassified in Dana 8th edition. There are no WO4 tetrahedra in it, so it should be classified as a simple oxide.
Hübnerite forms a complete solid solution series with ferberite.
Specific gravity: 7.12 to 7.18
Hardness: 4 to 4½
Streak: Greenish-grey, yellow to reddish-brown
Colour: Yellow-brown, reddish-brown, blackish brown, black, red (rare)
Environments:

Pegmatites
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Hübnerite occurs in high-temperature (hypothermal) hydrothermal veins and medium temperature metamorphic rocks. It also occurs in granite pegmatites and in alluvial and residual deposits.
Associated minerals include cassiterite, arsenopyrite, molybdenite, tourmaline, topaz, rhodochrosite and fluorite.

Humite

Formula: Mg7(SiO4)3(F,OH)2 nesosilicate (insular SiO4 groups)

Hydrocerussite

Formula: Pb3(CO3)2(OH)2 anhydrous carbonate containing hydroxyl
Specific gravity: 6.8
Hardness: 3½
Streak: White
Colour: White or grey; colourless in transmitted light
Solubility: Soluble in acids with effervescence
Environments:

Metamorphic environments
Hydrothermal environments

At the type locality cerussite occurs in a metamorphosed Mn-Fe deposit. It is usually a secondary mineral developed in the oxidised portions of lead deposits, but it can also be primary.

Alteration

In Tsumeb, Namibia, it is formed by the alteration of cerussite. This requires highly alkaline conditions with a pH of 10 to 13, and a constant and stable concentration of carbonate ions in solution. These conditions are most likely only at depth.
At the Higher Pitts Mine, Mendip Hills, England, hydrocerussite is fairly common as massive nodules, and also forms as an alteration product around nodules of mendipite.
At Långban, Sweden, hydrocerussite is most commonly found as an alteration product of native lead, associated with litharge, hausmannite or clinopyroxene skarn.

Litharge, CO2 and H2O to hydrocerussite
3PbO + 2CO2 + H2O → Pb3(CO3)2(OH)2
Synthetic hydrocerussite can be easily obtained, as a white powder, by the action of carbon dioxide and water on litharge at pH 4-5.

Hydroxylclinohumite

Formula: Mg9(SiO4)4(OH)2 nesosilicate (insular SiO4 groups)
Specific gravity: 3.13
Hardness: 6½
Streak: White
Colour: Pale yellow to orange-yellow, almost colourless
Environments:

Metamorphic environments

Hydroxylclinohumite occurs in skarn rims around dolomitic marble xenoliths in gabbroic rocks.

Alteration

diopside, dolomite and H2O ⇌ hydroxylclinohumite, calcite and CO2
2CaMgSi2O6 + 7CaMg(CO3)2 + H2O ⇌ 4Mg2SiO4.Mg(OH)2 + 9CaCO3 + 5CO2
In the nodular dolomites, hydroxylclinohumite associated with calcite occurs in a narrow zone in the central parts of the nodules due to the above reaction.

forsterite, dolomite and H2O to calcite, hydroxylclinohumite and CO2
4Mg2SiO4 + CaMg(CO3)2 + H2O → Mg9(SiO4)4(OH)2 +CaCO3 + CO2
A forsterite-clinohumite assemblage in the silica-rich dolomite in the aureole of the Alta granodiorite in Utah, USA, is probably due to the above reaction.

tremolite, dolomite and H2O ⇆ hydroxylclinohumite, calcite and CO2
Ca2Mg5Si8O22(OH)2 + 13CaMg(CO3)2 + H2O ⇆ 2(4Mg2SiO4.Mg(OH)2) + 15CaCO3 + 11CO2

Hypersthene

Hypersthene is a term used for a mineral part way between enstatite and ferrosilite. It is not a valid mineral name.
Formulae:
Hypersthene (Mg,Fe)SiO3
Enstatite MgSiO3
Ferrosilite FeSiO3
Properties of hypersthene:
Specific gravity:
Hardness: 5½ to 6
Streak: Greyish white, greenish
Colour: Greyish white
Solubility: Insoluble in water, nitric and sulphuric acid; soluble in hydrochloric acid
Environments:

Metamorphic environments

Hypersthene occurs in igneous rocks and schist and as pyroclasts (particles ejected during a volcanic eruption). It also may be found in basalt.

Alteration

augite and CO2 to hypersthene, calcite and quartz
Ca(Mg,Fe)Si2O6 + CO2 → (Mg,Fe)SiO3 + CaCO3 + SiO2

hypersthene, augite and Fe and Cr-rich spinel to garnet and olivine
2(Mg,Fe)SiO3 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4

jadeite, diopside, magnetite and quartz to aegirine, kushiroite (pyroxene) and hypersthene
2NaAlSi2O6 + CaMgSi2O6 + Fe2+Fe3+2O4 + SiO2 ⇌ 2NaFe3+Si2O6 + CaAlAlSiO6 + MgFeSi2O6
Aegirine in blueschist facies rocks may be formed by the above reaction.

Ilmenite

Formula: Fe2+Ti4+O3 simple oxide
Specific gravity: 4.68 to 4.76
Hardness: 5 to 6
Streak: Black to reddish brown
Colour: Black
Solubility: Slightly soluble in hydrochloric acid
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites (typical)
Sedimentary environments
Placer deposits

Ilmenite is a high-temperature primary mineral that is found in igneous environments and as a constituent of black sands.
It may be found in anorthosite, basalt, gabbro, kimberlite and syenite. As a constituent of black sands it is associated with magnetite, rutile, zircon and monazite.

It is a mineral of the granulite facies.

Alteration

Ilmenite may alter to hematite or rutile.

aenigmatite, anorthite and O2 to hedenbergite, albite, ilmenite and magnetite
½Na4[Fe2+10Ti2]O4[Si12O36] + CaAl2Si2O8 + ½O2 = CaFe2+Si2O6 + 2NaAlSi3O8 + Fe2+Ti4+O3 + Fe2+Fe3+2O4

amphibole, chlorite, paragonite, ilmenite, quartz and calcite to garnet, omphacite, rutile, H2O and CO2
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + Mg5Al(AlSi3O10)(OH)8 + 3NaAl2(Si3Al)O10(OH)2 + 4Fe2+Ti4+O3 + 9SiO2 + 4CaCO3 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 8H2O + 4CO2
In low-grade rocks relatively rich in calcite the garnet-omphacite association may be due to reactions such as the above.

amphibole, clinozoisite, chlorite, albite, ilmenite and quartz to garnet, omphacite, rutile and H2O
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + 2Ca2Al3[Si2o7][SiO4]O(OH) + Mg5Al(AlSi3O10)(OH)8 + 3NaAlSi3O8 + 4Fe2+Ti4+O3 + 3SiO2 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 6H2O
In low-grade rocks relatively poor in calcite the garnet-omphacite association may be developed by the above reaction.

augite, albite, pyroxene, anorthite and ilmenite to omphacite, garnet, quartz and rutile
2MgFe2+Si2O6 + Na(AlSi3O8) + Ca2Mg2Fe2+Fe3+AlSi5O18 + 2Ca(Al2Si2O8) + 2Fe2+Ti4+O3 → NaCa2MgFe2+Al(Si2O6)3 + (Ca2Mg3Fe2+4)(Fe3+Al5)(SiO4)9 + SiO2 + 2TiO2
This reaction occurs at high temperature and pressure.

titanomagnetite (ilmenite combined with magnetite), quartz, and aegirine-hedenbergite to aenigmatite, hedenbergite, magnetite and O2
6(Fe2+Ti4+O3 + Fe2+Fe3+2O4) + 12SiO2 + 12(NaFe3+Si2O6 + CaFe2+Si2O6) ⇌ 3Na4[Fe2+10Ti2]O4[Si12O36] + 12CaFe2+Si2O6 + 2Fe2+Fe3+2O4 + 5O2

Common impurities: Mn,Mg,V

Imogolite

Formula: Al2SiO3(OH)4 phyllosilicate (sheet silicate), allophane group
Specific gravity: 2.7
Hardness: 2 to 3
Streak: White
Colour: Yellowish white, light brownish yellow, blue, green, brown
Environments:

Sedimentary environments

Imogolite occurs principally in soils derived from volcanic ash. It has been found associated with allophane, halloysite, vermiculite, goethite, gibbsite and quartz. Imogolite has been observed in cracks in weathered plagioclase.

Jacobsite

Formula: Mn2+Fe3+2O4 multiple oxide, spinel group
Jacobsite forms a series with magnetite
Specific gravity: 4.76
Hardness: 5½ to 6½
Streak: Reddish black or brownish black
Colour: Black, gray in reflected light
Epitaxy: Jacobsite forms oriented intergrowths with hausmannite.
Environments:

Sedimentary environments
Metamorphic environments

Jacobsite is a primary mineral or a secondary alteration product of other manganese-bearing minerals in some metamorphosed manganese deposits, associated with hausmannite, galaxite, braunite, pyrolusite, coronadite, hematite or magnetite.
In Sweden jacobite occurs in crystalline limestone with native copper at the Jakobsberg mine, and with tephroite and calcite at Långban. The Hutter Mine locality, Pittsylvania County, Virginia, is a metamorphosed magnetite deposit, with subsidiary manganoan marble, that occurs in schist. Manganese oxides and spinel group minerals at the Hutter Mine include hausmannite, magnetite, galaxite and jacobsite. It seems that the maximum temperature developed here was 550 to 600oC.

Common impurities: Zn

Jadeite

Formula:NaAlSi2O6 inosilicate (chain silicate) pyroxene group
Specific gravity: 3.25 to 3.35
Hardness: 6
Streak: White
Colour: apple-green, greenish white, purplish blue, blue-green
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments:

Metamorphic environments

Jadeite is found only in metamorphic rocks. It is a characteristic mineral of the blueschist facies, where it may be associated with glaucophane.

Alteration

albite, chlorite and calcite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz, CO2 and H2O
8Na(AlSi3O8) + (Mg4.0Fe2.0)(AlSi3O10)(OH)8 + CaCO3 → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 2SiO2 + CO2 + 2H2O
In low to intermediate metamorphism jadeite-glaucophane assemblages may arise from reactions such as the one above.

albite and montmorillonite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz and H2O
8Na(AlSi3O8) + 2Ca0.5(Mg3.5Al0.5)Si8O20(OH)4.nH2O → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 15SiO2 +6H2O
This reaction occurs in low to intermediate metatmorphism.

anorthite, albite and H2O to jadeite, lawsonite and quartz
CaAl2 Si2O8 + NaAlSi3O8 + 2H2O → NaAlSi2O6 + CaAl2(Si2O7)(OH)2.H2 + SiO2

jadeite to nepheline and albite
2NaAlSi2O6 ⇌ NaAlSiO4 + NaAlSi3O8
At 20 kbar pressure the equilibrium temperature is about 1,000oC (eclogite facies), with equilibrium to the right at higher temperatures and to the left at lower temperatures.

jadeite, diopside, magnetite and quartz to aegirine, kushiroite (pyroxene) and hypersthene
2NaAlSi2O6 + CaMgSi2O6 + Fe2+Fe3+2O4 + SiO2 ⇌ 2NaFe3+Si2O6 + CaAlAlSiO6 + MgFeSi2O6
Aegirine in blueschist facies rocks may be formed by the above reaction.

jadeite and quartz to albite
NaAlSi2O6 + SiO2 ⇌ NaAlSi3O8
High pressure favours the reverse reaction. Sometimes found in blueschist metamorphic rocks.

lawsonite and jadeite to clinozoisite, paragonite, SiO2 and H2O
4CaAl2(Si2O7)(OH)2.H2 + NaAlSi2O6 ⇌ 2Ca2Al3[Si2o7][SiO4]O(OH) + NaAl2(Si3Al)O10(OH)2 + SiO2 +6H2
Clinozoisite and paragonite may have been derived from lawsonite by the above reaction.

Common impurities: Ti,Mn,Mg,Ca,K,H2O

Jarosite

Formula: KFe3+3(SO4)2(OH)6 sulphate, alunite group
Specific gravity: 2.9 to 3.3
Hardness: 3 to 4
Streak: Yellow
Colour: Ochre-yellow, brown to blackish brown
Solubility: Moderately soluble in hydrochloric acid
Environments:

Hydrothermal environments

Jarosite is a secondary mineral found in the oxidation zone of hypothermal (high temperature) veins and sulphide deposits, formed by weathering in arid climates.

Common impurities: Na,Ag,Pb

Johannsenite

Formula: CaMnSi2O6 inosilicate pyroxene
Specific gravity: 3.56
Hardness: 6
Streak: White
Colour: Blue-green, grey-white, dark brown, colourless
Environments:

Metamorphic environments

Johannsenite is found in contact metamorphic environments

Alteration

johansennite and H2O to rhodonite and xonotlite
6CaMnSi2O6 + H2O → 6Mn2+SiO3 + Ca6Si6O17(OH)2
At Pueblo, Mexico, johansennite occurs in calcite veins in rhyolite and is altered to rhodonite and xonotlite according to the above equation.

Common impurities: Ti,Al,Fe,Mg,Na,K,C,P,H2O

Junitoite

Formula: CaZn2Si2O7.H2O
Sorosilicate
Specific gravity: 3.5
Hardness: 4½
Streak: Colourless
Colour: Colourless to milky white
Environments

Metamorphic environments

At the type locality, the Christmas mine, Gila county, Arizona, USA, junitoite occurs in a retrogressively altered skarn, with its occurrence closely related to the breakdown of sphalerite in the ores. It is associated with kinoite, apophyllite, tyrolite, sphalerite, clay minerals, calcite, and xonotlite.

K-feldspar

K-feldspars include microcline, orthoclase and sanidine, all of which have the formula KAlSi3O8 tectosilicates (framework silicates)
Specific gravity: 2.54 to 2.63
Hardness: 6 to 6 1/2
Streak: White
Colour: Colourless, white, grey, greyish yellow, yellowish, tan, pink, bluish green, greenish white, reddish white
Melting point: About 1,300oC at atmospheric pressure
Environments

Plutonic igneous environments
Volcanic igneous environments
Metamorphic environments
Hydrothermal environments

K-feldspars are essential constituents of rhyolite and common constituents of quartzolite.
They also may be found in diorite.
K-feldspars are minerals of the hornblende-hornfels, greenschist and amphibolite facies.

Alteration

K-feldspar is a major alteration phase in many ore deposits, but most common in porphyry (rock with coarse phenocrysts in a finer groundmass) metal deposits, usually formed early in the sequence. In high temperature alteration the K-feldspar that forms is usually orthoclase, and at lower temperatures it is usually microcline.

dolomite, K-feldspar and H2O to phlogopite, calcite and CO2
3CaMg(CO3)2 + KAlSi3O8 + H2O = KMg3AlSi3O10(OH)2 + 3CaCO3 + 3CO2
In the presence of Al and K the metamorphism of dolomite leads to the formation of phlogopite according to the above equation.

enstatite-ferrosilite, K-feldspar and H2O to biotite and quartz
3(Mg,Fe2+)SiO3 + K(AlSi3O8) + H2O ⇌ K(Mg,Fe)3(AlSi3O10)(OH)2+ 3SiO2
The forward reaction leads to an amphibolite facies assemblage.

K-feldspar and H+ to muscovite, quartz and K+
3KaAlSi3O8 + 2H+ ⇌ KAl2(AlSi3O100(OH)2 + 6SiO2 + 2K+
Low temperature and a low K+/H+ ratio favour the forward reaction.

montmorillonite and K-feldspar to illite (variety of muscovite), SiO2 and H2O
Al2Si4O10(OH)2.nH2 + KAl2(AlSi3)O10(OH)2 + 4SiO2 + nH2O

muscovite to corundum, K-feldspar and H2O
KAl2(AlSi3O10)(OH)2 ⇌ Al2O3 + K(AlSi3O8) + H2O
This reaction takes place above temperatures ranging from 600oC at atmospheric pressure (hornblende-hornfels facies) to about 720oC at pressure above 4 kbar (amphibolite facies).

muscovite, biotite and SiO2 to K-feldspar, garnet and H2O
KAl2(AlSi3O10)(OH)2 + K(Fe2+,Mg)3(AlSi3O10)(OH)2 + 3SiO2 → 2KAlSi3O8 + (Fe2+,Mg)3Al2(SiO4)3 + 2H2O

muscovite and quartz to sillimanite, K-feldspar and H2O
KAl2(Si3Al)O10(OH)2 + SiO2 ⇌ Al2SiO5 + KAlSi3O8 + H2O
At 5 kbar pressure the equilibrium temperature is about 690oC (amphibolite facies)
The forward reaction is strongly endothermic (absorbs heat) and the reverse reaction in exothermic (gives out heat), hence the forward reaction is favoured by high temperatures, as the system adjusts to bring the temperature back down.
Although the muscovite-quartz assemblage is stable over a large part of the PT range of regional metamorphism, at temperatures around 600 to 650oC it is replaced by sillimanite and K-feldspar.

Common impurities: Fe,Ca,Na,Li,Cs,Rb,H2O,Pb

Kalsilite

Formula:KAlSiO4
Tectosilicate (framework silicate), feldspathoid
Specific gravity: 2.6
Hardness: 6
Streak: White
Colour: colourless, grey, grey white, white
Environments:

Plutonic igneous environments
Volcanic igneous environments

Kalsilite is found as embedded grains in silica-undersaturated lavas and nepheline-bearing igneous rocks, associated or intergrown with nepheline.

Common impurities: Fe,Mg,Ca,Na

Kaolinite

Formula: Al2Si2O5(OH)4 phyllosilicate (sheet silicate)
Specific gravity: 2.6
Hardness: 2 to 2½
Streak: white
Colour: white, brownish white, greyish white, yellowish white, greyish green
Solubility: Insoluble in water, nitric and sulphuric acid; soluble with decomposition in hydrochloric acid
Environments:

Sedimentary environments
Metamorphic environments
Hydrothermal environments

Kaolinite is always a secondary mineral derived from weathering or hydrothermal alteration of alumino-silicate minerals. It is a mineral of the zeolite facies, where clay minerals transform to illite (variety of muscovite), kaolinite and vermiculite. It is also a mineral of the prehnite-pumpellyite, greenschist and albite-epidote-hornfels facies.

Alteration

anorthite, H2SO4 and H2O to gypsum and kaolinite
CaAl2 Si2O8 + H2SO4 + 3H2O → CaSO4.2H2O + Al2Si2O5(OH)4

anorthite to calcite and kaolinite in the early Earth's atmosphere
CO2 + H2O + anorthitecalcite + kaolinite
CO2 + 2H2O + CaAl2Si2O8 → CaCO3 + Al2Si2O5(OH)4

anorthite, H2O and CO2 ⇌ kaolinite and calcite
2CaAl2 Si2O8 + 4H2O + 2CO2 ⇌ Al4Si4O10(OH)8 + 2CaCO3
calcite is found as a low-temperature, late-stage alteraation product according to the above reaction.

kaolinite to andalusite, pyrophyllite and H2O
3Al2Si2O5(OH)4 ⇌ 2Al2OSiO4 + Al2Si4O10(OH)2 + 5H2O
At 1 kbar pressure the equilibrium temperature for the reaction is about 320oC (albite-epidote-hornfels facies), with the equilibrium to the right at higher temperatures and to the left at lower temperatures.

kaolinite to diaspore, SiO2 and H2O
Al2Si2O5(OH)4 ⇌ 2AlO(OH) + 2SiO2 (aqueous) + H2O
At 10 kbar pressure the equilibrium temperature is about 300oC (blueschist facies).
At 1 kbar pressure kaolinite is stable at temperatures less than 300oC; it can be in equilibrium with quartz and water in solutions both saturated and undersaturated with quartz. Diaspore is stable at temperatures less than 400oC but only in solutions undersaturated with quartz. High temperature and low quartz saturation favours the forward reaction.

kaolinite to kyanite, pyrophyllite and H2O
3Al2Si2O5(OH)4 ⇌ 2Al2OSiO4 + Al2Si4O10(OH)2 + 5H2O
At 5 kbar pressure the equilibrium temperature for the reaction is about 375oC (greenschist facies), with the equilibrium to the right at higher temperatures and to the left at lower temperatures.

kaolinite to pyrophyllite, diaspore and H2O
2Al2Si2O5(OH)4 → Al2Si4O10(OH)2 + 2AlO(OH) + 2H2O
In the absence of quartz, kaolinite breaks down on heating according to the above reaction.
At 5 kbar pressure the equilibrium temperature for the reaction is about 320oC (prehnite-pumpellyite facies), and at 9 kbar it is about 380oC (greenschist facies).

kaolinite and H2O to gibbsite and quartz
Al2Si2O5(OH)4 + H2O ⇌ 2Al(OH)3 + 2SiO2

kaolinite and diaspore to andalusite and H2O
Al2Si2O5(OH)4 + 2AlO(OH) ⇌ 2Al2OSiO4 + 3H2O
At 1 kbar pressure the equilibrium temperature for the reaction is about 320oC (albite-epidote-hornfels facies), with the equilibrium to the right at higher temperatures and to the left at lower temperatures.

kaolinite and diaspore to kyanite and H2O
Al2Si2O5(OH)4 + 2AlO(OH) ⇌ 2Al2OSiO4 + 3H2O
At 5 kbar pressure the equilibrium temperature for the reaction is about 370oC (greenschist facies), with the equilibrium to the right at higher temperatures and to the left at lower temperatures.

kaolinite, dolomite, quartz and H2O to chlorite, calcite and CO2
Al2Si2O5(OH)4 + 5CaMg(CO3)2 + SiO2 + 2H2O ⇌ Mg5Al(AlSi3O10)(OH)8 + 5CaCO3 + 5CO2
Chlorite often forms in this way from reactions between clay minerals such as kaolinite and carbonates such as dolomite.

kaolinite and quartz to pyrophyllite and H2O
Al2Si2O5(OH)4 + 2SiO2 → Al2Si4O10(OH)2 + H2O
This reaction represents the breakdown of kaolinite in the presence of quartz. (If quartz is absent, diaspore is formed as well as pyrophyllite).
At 5 kbar pressure the equilibrium temperature is about 340oC (prehnite-pumpellyite facies), and at 10 kbar it is about 300oC (blueschist facies).

lawsonite and kaolinite to margarite, pyrophyllite and H2O
CaAl2(Si2O7)(OH)2.H2 + 2Al2Si2O5(OH)4 ⇌ CaAl2(Al2Si2O10)(OH)2 + Al2Si4O10(OH)2 + 4H2O
The equilibrium temperature for this reaction at 5 kbar pressure is about 360oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and kaolinite to margarite, quartz and H2O
CaAl2(Si2O7)(OH)2.H2 + Al2Si2O5(OH)4 ⇌ CaAl2(Al2Si2O10)(OH)2 + 2SiO2 +3H2O
The equilibrium temperature for this reaction at 2 kbar pressure is about 300oC (prehnite-pumpellyite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

pyrophyllite and H2O to kaolinite and aqueous SiO2
Al2Si2O10(OH)2 + H2O → Al2Si2O5(OH)4 + 2SiO2
At 1 kbar pressure kaolinite is stable at temperatures less than 300oC; it can be in equilibrium with quartz and water in solutions both saturated and undersaturated with quartz. Pyrophyllite is stable at temperatures up to 450oC and above, but except for a very narrow band of temperature and composition, it is stable only with solutions supersaturated with quartz

kaolinite to pyrophyllite, diaspore and H2O
2Al2Si2O5(OH)4 → Al2Si4O10(OH)2 + 2AlO(OH) + 2H2O
In the absence of quartz, kaolinite breaks down on heating according to the above reaction.

muscovite, H+ and H2O to kaolinite and K+
2KAl2(AlSi3O10)(OH)2 + 2H+ + 3H2O ⇌ 3Al2Si2O5(OH)4 + 2K+
Low temperature and a low K+/H+ ratio favour the forward reaction.

Common impurities: Fe,Mg,Na,K,Ti,Ca,H2O

Kegelite

Formula: Pb42Si4O10(SO4)(CO3)2(OH)4 phyllosilicate (sheet silicate)

Kernite

Formula: Na2B4O6<(OH)2.3H2O borate
Specific gravity: 1.9
Hardness: 2½ to 3
Streak: White
Colour: When fresh colourless and transparent, but usually white and opaque
Solubility: Slightly soluble in water; readily soluble in hydrochloric, sulphuric and nitric acid
Environments:

Sedimentary environments

Kernite occurs in chemical sedimentary environments associated with colemanite and ulexite. The kernite is believed to have formed from borax.
It alters to tincalconite on dehydration.

Kinoite

Formula: Ca22Si3O10.2H2O
Sorosilicate
Specific gravity: 3.13 to 3.19
Hardness: 2½
Streak: Light blue
Colour: Azure blue
Solubility: Decomposed by hydrochloric acid
Environments:

Metamorphic environments
Hydrothermal environments
Basaltic cavities

At the Christmas mine, Gila county, Arizona, USA, kinoite is associated with apophyllite and ruizite.
At Helvetia, Pima county, Arizona, USA, kinoite is associated with apophyllite.
At the type locality, the Santa Rita Mountains, Pima County, Arizona, USA, kinoite occurs in veinlets and as crystals embedded in apophyllite in mineralised, brecciated diopside-garnet-calcite-quartz skarn , associated with apophyllite, native copper and copper sulphide minerals. It is clearly contemporaneous with apophyllite and of primary origin . Also native copper is found embedded in apophyllite crystals with kinoite.
At the Twin Buttes mine, Pima County, Arizona, USA, kinoite is associated with stringhamite, native copper, wollastonite, and an apophyllite group mineral.
Kinoite from Arizona is related to late-stage retrograde activity that altered a skarn mineral assemblage composed of diopside, grossular, calcite, and quartz. Less common accessory minerals include gilalite, apachite, stringhamite, junitoite, clinohedrite and xonotlite.
At Calumet, Michigan, USA, kinoite occurs in vesicles in basaltic lava flows and enclosed in quartz and calcite. It is associated with quartz, calcite, native copper, native silver, epidote, pumpellyite, saponite, datolite and chlorite.

Common impurities: Mg

Kintoreite

Formula: PbFe3+3(PO4)(PO3OH)(OH)6
Forms a solid-solution series with corkite.
Specific gravity: 4.34 (calculated)
Hardness: 4
Streak: Pale yellowish green
Colour: Cream to yellowish green and brownish yellow
Occurrence: Crusts line cavities in goethite. Encrustations on quartz and garnet-rich lode rocks.

Kolbeckite

Formula: Sc(PO4).2H2O hydrated normal phosphate, variscite group
Specific gravity: 2.35
Hardness: 3 to 5
Streak: White
Colour: Colourless, light yellow; when impure: cyan-blue, blue-gray, apple-green
Solubility: Decomposed by acids
Environments:

Hydrothermal environments

Kolbeckite is a very rare secondary mineral in phosphate deposits and some hydrothermal veins. It is found in a quartz hübnerite-ferberite vein at the type locality, the Sadisdorf copper mine, Saxony, Germany.

Kolicite

Formula: Zn4Mn2+7(AsO4)2(SiO4)2(OH)8
Compound arsenate
Specific gravity: 4.17
Hardness: 4½
Streak: Pale orange
Colour: Orange
Environments:

Metamorphic environments

Kolicite is rare at the type locality, the Sterling Mine, New Jersey, USA, where it has been found in a marble-hosted zinc oxide and zinc silicate orebody, associated with willemite, holdenite, franklinite, calcite, sonolite and friedelite.

Common impurities: Fe,Mg,H2O

Kraisslite

Formula: Zn3(Mn,Mg)25(Fe3+,Al)(As3+O3)2 [(Si,As5+)O4]10
Compound arsenate
Specific gravity: 3.876
Hardness: 3 to 4
Streak: Golden brown
Colour: Deep copper brown
Environments:

Metamorphic environments
Hydrothermal environments

Kraisslite occurs as a secondary mineral in micaceous veinlets and fracture fillings in the zincite zone of a metamorphosed zinc deposit, associated with zincite, willemite, sussexite, sphalerite, rhodochrosite, pyrochroite, franklinite, baryte and austinite.

Common impurities: Al,H2O

Kyanite

Formula: Al2OSiO4 nesosilicate (insular SiO4 groups). Polymorph (same formula, different structure) of andalusite and sillimanite.
Specific gravity: 3.53 to 3.65
Hardness: 5½ to 7
Streak: White
Colour: Blue, green, orange, black
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Placer deposits
Metamorphic environments (typical)

Kyanite is a common mineral of high to very high pressure regionally metamorphosed rocks and typically it is found in gneiss and schist. It is often associated with garnet, staurolite and corundum.
It is a common constituent of eclogite, and it also may be found in hornfels and in garnet- omphacite-kyanite occurrences in kimberlite pipes.
Kyanite develops after staurolite and before sillimanite with increasing grade of metamorphism. It is a characteristic mineral of the amphibolite and granulite facies and it is also a mineral of the greenschist, blueschist and eclogite facies.

Alteration

Aluminium silicate stability diagram Andalusite, sillimanite and kyanite are polymorphs (same formula, different structure); they are in equilibrium at a pressure of 3.75 kbar and temperature 504oC (amphibolite facies).
Kyanite is unstable at low pressure.

anorthite to grossular, kyanite and quartz
3CaAl2 Si2O8 → Ca3Al2(SiO4)3 + 2Al2OSiO4 + SiO2
At 20 kbar pressure the equilibrium temperature is about 1,000oC and at 30 kbar it is about 1,400oC

diaspore and quartz to kyanite and H2O
2AlO(OH) + SiO2 ⇌ Al2OSiO4 + H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 420oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

enstatite, kyanite and quartz to cordierite
Mg2Si2O6 + 2Al2OSiO4 + SiO2 ⇌ Mg2Al4Si5O18
At 6 kbar pressure the equilibrium temperature is about 475oC (greenschist facies). The equilibrium moves to the right at higher temperatures and to the left at lower temperatures

forsterite, kyanite and quartz to cordierite
Mg2SiO4 + 2Al2OSiO4 + 2SiO2 ⇌ Mg2Al4Si5O18
At 6 kbar pressure the equilibrium temperature is about 400oC (greenschist facies).

grossular and kyanite to anorthite and corundum
Ca3Al2(SiO4)3 + 3Al2OSiO4 ⇌ 3CaAl2Si2O8 + Al2O3
The equilibrium temperature for this reaction at 10 kbar pressure is about 540oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

grossular, kyanite and quartz to anorthite
Ca3Al2(SiO4)3 + 2Al2OSiO4 + SiO2 ⇌ 3CaAl2Si2O8
The equilibrium temperature for this reaction at 10 kbar pressure is about 510o (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

kaolinite to kyanite, pyrophyllite and H2O
3Al2Si2O5(OH)4 ⇌ 2Al2OSiO4 + Al2Si4O10(OH)2 + 5H2O
At 5 kbar pressure the equilibrium temperature for the reaction is about 375oC (greenschist facies), with the equilibrium to the right at higher temperatures and to the left at lower temperatures.

kaolinite and diaspore to kyanite and H2O
Al2Si2O5(OH)4 + 2AlO(OH) ⇌ 2Al2OSiO4 + 3H2O
At 5 kbar pressure the equilibrium temperature for the reaction is about 370oC (greenschist facies), with the equilibrium to the right at higher temperatures and to the left at lower temperatures.

kyanite and enstatite to cordierite and corundum
3Al2O(SiO4) + Mg2Si2O6 ⇌ Mg2Al4Si5O18 + Al2O3
The equilibrium temperature for this reaction at 6 kbar pressure is about 520oC (amphibolite facies), with equilibrium to the right at higher temperatures, and to the left at lower temperatures.

kyanite and enstatite to quartz and pyrope
2Al2O(SiO4) + 3Mg2Si2O6 ⇌ 2SiO2 + 2Mg3Al2(SiO4)3
The equilibrium temperature for this reaction at 14 kbar pressure is about 950oC (granulite facies), with equilibrium to the right at higher temperatures, and to the left at lower temperatures.

kyanite and zoisite to anorthite, corundum and H2O
2Al2O(SiO4) + 2Ca2Al3[Si2O7][SiO4]O(OH) ⇌ 4CaAl2Si2O8 + Al2O3 + H2O
The equilibrium temperature for this reaction at 5 kbar pressure is 480oC (greenschist facies), and at 10 kbar it is about 720oC (amphibolite facies). The equilibrium is to the right at higher temperatures, and to the left at lower temperatures.

kyanite and zoisite to margarite and anorthite
2Al2O(SiO4) + 2Ca2Al3[Si2O7][SiO4]O(OH) ⇌ CaAl2(Al2Si2O10)(OH)2 + Ca(Al2Si2O8)
The equilibrium temperature for this reaction at 6 kbar pressure is about 520oC (amphibolite facies), and at 9 kbar it is about 675oC (amphibolite facies). At any pressure the euqilibrium is displaced to the right at higher temperatures, and to the left at lower temperatures.

lawsonite to zoisite, kyanite, quartz and H2O
4CaAl2(Si2O7)(OH)2.H2 ⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + Al2OSiO4 + SiO2 + 7H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 500oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and corundum to zoisite, kyanite and H2O
4CaAl2(Si2O7)(OH)2.H2 + Al2O3 ⇌ 2Ca2Al3[Si2O7][SiO4}O(OH) + 2Al2OSiO4 + 7H2O
The equilibrium temperature for this reaction at 15 kbar pressure is about 570oC(eclogite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and kyanite to margarite, pyrophyllite and H2O
3CaAl2(Si2O7)(OH)2.H2 + 4Al2OSiO4 ⇌ 3CaAl2(Al2Si2O10)(OH)2 + Al2Si4O10(OH)2 + 2H2O
The equilibrium temperature for this reaction at 6.5 kbar pressure is about 390oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and kyanite to margarite, quartz and H2O
CaAl2(Si2O7)(OH)2.H2 + Al2OSiO4 ⇌ CaAl2(Al2Si2O10)(OH)2 + SiO2 + H2O
The equilibrium temperature for this reaction at 8 kbar pressure is about 450oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and margarite to zoisite, kyanite and H2O
3CaAl2(Si2O7)(OH)2.H2 + CaAl2(Al2Si2O10)(OH)2 ⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + 2Al2OSiO4 + 6H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 500oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite to corundum, zoisite, kyanite and H2O
4CaAl2(Al2Si2O10)(OH)2 ⇌ 3Al2O3 + 2Ca2Al3[Si2O7][SiO4]O(OH) + 2Al2OSiO4 + 3H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 650oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite and quartz to anorthite, kyanite and H2O
CaAl2(Al2Si2O10)(OH)2 + SiO2 ⇌ Ca(Al2Si2O8) + Al2OSiO4 + H2O
The equilibrium temperature for this reaction at 5 kbar pressure is about 520oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite and quartz to zoisite, kyanite and H2O
4CaAl2(Al2Si2O10)(OH)2 + 3SiO2 ⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + 5Al2OSiO4 + 3H2O
The equilibrium temperature for this reaction at 8 kbar pressure is about 510oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

pyrophyllite to kyanite, quartz and H2O
Al2Si2O10(OH)2 ⇌ Al2OSiO4 + 3SiO2 + H2O
At 9 kbar pressure the equilibrium temperature is about 425oC (greenschist facies).

pyrophyllite and diaspore to kyanite and H2O
Al2Si4O10(OH)2 + 6AlO(OH) ⇌ 4Al2OSiO4 + 4H2O
This reacton is a higher pressure reaction, occurring above about 1.9 kbar. Increasing temperature favours the forward reaction. At 9 kbar pressure the equilibrium temperature is about 380oC (greenschist facies).

talc and kyanite to cordierite, corundum and H2O
2Mg3Si4O10(OH)2 + 7Al2OSiO4 ⇌ 3Mg2Al4Si5O18 + Al2O3 + 2H2O

zoisite, kyanite and diaspore to margarite
Ca2Al3[Si2O7][SiO4]O(OH) + Al2OSiO4 + 3AlO(OH) ⇌ 2CaAl2(Al2Si2O10)(OH)2
The equilibrium temperature for this reaction at 12 kbar pressure is about 480oC (blueschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

zoisite, kyanite and quartz to anorthite and H2O
2Ca2Al3[Si2O7][SiO4]O(OH) + Al2OSiO4 + SiO2 ⇌ 4Ca(Al2Si2O8) + H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 690oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

Langite

Formula: Cu4(SO4)(OH)6.2H2O hydrated sulphate containing hydroxyl
Specific gravity: 3.48 to 3.5
Hardness: 2½ to 3
Streak: Greenish blue
Colour: Blue, greenish-blue
Solubility: Insoluble in water. Readily soluble in acids or ammonia
Environments

Hydrothermal environments

Langite is a secondary copper mineral formed from the oxidation of copper sulphides, often as a post-mining deposit, typically found within oxidised copper-bearing veinstone within mine dumps and underground as flowstone on mine walls.

Lanarkite

Formula: Pb2O(SO4)
Anhydrous sulphate
Specific gravity: 6.92
Hardness: 2 to 2½
Streak: White
Colour: Grey to greenish white, pale yellow
Solubility: Soluble in KOH and in warm nitric acid
Environments:

Hydrothermal environments

Lanarkite is a rare secondary supergene mineral in the oxidised zone of galena deposits, associated with cerussite, leadhillite, susannite, hydrocerussite and caledonite.
Lanarkite requires an unusually high pH (very alkaline environment) for its formation.
It alters to cerussite, leadhillite and anglesite.
At Balliway Rigg, Caldbeck Fells, Cumbria, England, UK, a small number of lanarkite specimens were found in an oxidised galena vein. Some crystals are completely replaced by leadhillite, and leadhillite epimorphs after lanarkite are present on a number of specimens. Drusy mattheddleite commonly overgrows lanarkite and it is occasionally associated with caledonite. Although many of the specimens are associated with partly oxidised galena, galena is not present in every case.
At the Driggith mine, Caldbeck Fells, Cumbria, England, UK, lanarkite has been found on two specimens in cavities in corroded galena. On one specimen lanarkite is associated with leadhillite, anglesite and chenite and in the second with anglesite.
At Silver Gill, Caldbeck Fells, Cumbria, England, UK, lanarkite was identified on a single specimen as minute crystals in a quartz cavity containing remnant galena.
At the type locality, the Susanna mine, Leadhills, Scotland, UK, lanarkite is associated with leadhillite, cerussite and caledonite.
At the the Gallagher Vanadium Property and Manila Mine, Cochise County, Arizona, USA, lanarkite has been found in one occurrence as small crystals on leadhillite and anglesite in the altered crust of a galena nodule.

Laumontite

Formula: CaAl2Si4O12.4H2O tectosilicate (framework silicate), zeolite group
Specific gravity: 2.23 to 2.41
Hardness: 3½ to 4
Streak: White
Colour: White, brown, yellow, pink
Solubility: Moderately soluble in hydrochloric acid
Environments:

Pegmatites
Sedimentary environments
Metamorphic environments
Basaltic cavities

Laumontite is a zeolite facies mineral, formed by the decomposition of analcime. When it is associated with prehnite it forms in the transition zone between the zeolite and greenschist facies
Geothermal wells have been drilled through a thick series of basalt flows in western Iceland, where it was found that laumontite crystallised at temperatures from 98oC to 230oC.
Authigenic (formed in place) laumontite has been reported forming part of the cementing material in sandstone, and it has also been found as a secondary mineral in sandstone.

Alteration

laumontite to lawsonite, quartz and H2O
CaAl2Si4O12.4H2O→ CaAl2(Si2O7)(OH)2.H2O + 2SiO2 + 2H2O
In subduction zones, as the pressure rises to above about 1.5 kbar, laumontite alters to lawsonite according to the above reaction.

laumontite and calcite to prehnite, quartz, H2O and CO2
CaAl2Si4O12.4H2O + CaCO3 → Ca2Al(Si3Al)O10(OH)2 + SiO2 + 3H2O + CO2
Prehnite and pumpellyite form from calcium zeolites in the presence of calcite, as in the above equation.

Common impurities: Na,K,Fe

Lavendulan

Formula: NaCaCu5(AsO4)4Cl.5H2O
Hydrated arsenate containing halogen, lavendulan group, dimorph of lemanskiite
Specific gravity: 3.84
Hardness: 2½ to 3
Streak: Light blue
Colour: Lavender blue (Dana)
Environments:

Hydrothermal environments

lavendulan is a rare secondary mineral in the oxidised zone of some copper arsenic deposits.

At Joachimstal, Bolivia, lavendulan is associated with erythrite.

At San Juan, Chile, lavendulan is associated with erythrite, cuprite and malachite.

At the Cap Garonne mine, France, lavendulan is associated with chalcophyllite, cyanotrichite, parnauite, mansfieldite, olivenite, tennantite, covellite, chalcanthite, antlerite, brochantite and geminite.

At Bou Azzer, Morocco, lavendulan is associated with erythrite. At Tamdrost it is associated with pharmacosiderite and arseniosiderite. At Méchoui it has been found in dolostone associated with chalcocite, covellite and conichalcite. At Ightem it is associated with conichalcite, and at Oumlil it is associated with erythrite and scorodite.

At Imiter, Morocco, lavendulan has been found associated with erythrite.

At Tsumeb, Namibia, lavendulan is associated with cuprian adamite, conichalcite, o’danielite, tsumcorite, fahleite, quartz, calcite and gypsum.

At the San Rafael mine, Nye county, Nevada, USA, lavendulan is associated with scorodite.

Lawsonite

Formula: CaAl2(Si2O7)(OH)2.H2O sorosilicate (Si2O7 groups)
Specific gravity: 3.1
Hardness: 7½
Streak: White
Colour: Blue, white
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments:

Metamorphic environments

Lawsonite is a common constituent of gneiss and schist formed under low temperature and high pressure. It is a typical mineral of glaucophane schist, associated with chlorite, epidote, titanite, glaucophane, garnet and quartz.
Lawsonite also may be found in gneiss.

It is a mineral of the prehnite-pumpellyite, greenschist, blueschist and eclogite facies.

Alteration

anorthite, albite and H2O to jadeite, lawsonite and quartz
CaAl2 Si2O8 + NaAlSi3O8 + 2H2O → NaAlSi2O6 + CaAl2(Si2O7)(OH)2.H2O + SiO2

laumontite to lawsonite, quartz and H2O
CaAl2Si4O12.4H2O→ CaAl2(Si2O7)(OH)2.H2O + 2SiO2 + 2H2O
In subduction zones, as the pressure rises to above about 1.5 kbar, laumontite alters to lawsonite according to the above reaction.

lawsonite to zoisite, kyanite, quartz and H2O
4CaAl2(Si2O7)(OH)2.H2 ⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + Al2OSiO4 + SiO2 + 7H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 500oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite to zoisite, margarite, quartz and H2O
5CaAl2(Si2O7)(OH)2.H2 ⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + CaAl2(Al2Si2O10)(OH)2 + 2SiO2 + 8H2O
The equilibrium temperature for this reaction at 6.5 kbar pressure is about 425oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and corundum to zoisite, kyanite and H2O
4CaAl2(Si2O7)(OH)2.H2 + Al2O3 ⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + 2Al2OSiO4 + 7H2O
The equilibrium temperature for this reaction at 15 kbar pressure is about 570oC (eclogite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and diaspore to margarite and H2O
CaAl2(Si2O7)(OH)2.H2O + 2AlO(OH) ⇌ CaAl2(Al2Si2O10)(OH)2 + 2H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 460oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and jadeite to clinozoisite, paragonite, quartz and H2O
4CaAl2(Si2O7)(OH)2.H2 + NaAlSi2O6 ⇌ 2Ca2Al3[Si2o7][SiO4]O(OH) + NaAl2(Si3Al)O10(OH)2 + SiO2 +6H2

lawsonite and kaolinite to margarite, pyrophyllite and H2O
CaAl2(Si2O7)(OH)2.H2 + 2Al2Si2O5(OH)4 ⇌ CaAl2(Al2Si2O10)(OH)2 + Al2Si4O10(OH)2 + 4H2O
The equilibrium temperature for this reaction at 5 kbar pressure is about 360oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and kaolinite to margarite, quartz and H2O
CaAl2(Si2O7)(OH)2.H2 + Al2Si2O5(OH)4 ⇌ CaAl2(Al2Si2O10)(OH)2 + 2SiO2 +3H2O
The equilibrium temperature for this reaction at 2 kbar pressure is about 300oC (prehnite-pumpellyite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and kyanite to margarite, pyrophyllite and H2O
3CaAl2(Si2O7)(OH)2.H2 + 4Al2OSiO4 ⇌ 3CaAl2(Al2Si2O10)(OH)2 + Al2Si4O10(OH)2 + 2H2O
The equilibrium temperature for this reaction at 6.5 kbar pressure is about 390oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and kyanite to margarite, quartz and H2O
CaAl2(Si2O7)(OH)2.H2 + Al2OSiO4 ⇌ CaAl2(Al2Si2O10)(OH)2 + SiO2 + H2O
The equilibrium temperature for this reaction at 8 kbar pressure is about 450oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and margarite to zoisite, kyanite and H2O
3CaAl2(Si2O7)(OH)2.H2 + CaAl2(Al2Si2O10)(OH)2 ⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + 2Al2OSiO4 + 6H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 500oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

Lead

Formula: Pb native element
Specific gravity: 11.37
Hardness: 1½
Streak: Grey
Colour: Grey, but often coated with white hydrocerussite
Environments:

Placer deposits
Metamorphic environments
Hydrothermal environments

Native lead is a rare mineral of hydrothermal origin, and found in placers

Leadhillite

Formula: Pb4(SO4)(CO3)2(OH)2 compound carbonate
Polymorphs susannite and macphersonite
Hardness: 2½ to 3
Streak: White
Colour: Colourless to white, grey, yellowish, pale green to blue; colourless in transmitted light
Solubility: Soluble in nitric acid with effervescence, rendering a residue of lead sulphate. Exfoliates in hot water.
Environments:

Hydrothermal environments

Leadhillite occurs with mimetite and melanotekite at Tsumeb, Namibia.

At the Manila Mine in Arizona, USA, it occurs associated with anglesite, and in vugs with caledonite, diaboleite, linarite and lanarkite.

It is found at several localities in Cumbria, England:
At Balliway Rigg it has been found in cavities in oxidised galena in quartz veins, associated with caledonite, mattheddleite Pb5(SiO4)1.5(SO4)1.5Cl and lanarkite. It is sometimes associated with anglesite, cerussite or linarite.
At Red Gill Mine it occurs as crusts on quartz associated with numerous minerals including anglesite, linarite, caledonite, bindheimite Pb2Sb5+2O7, cerussite and susannite.
At Shortgrain leadhillite is common in the supergene post-mining assemblage, and in some specimens it replaces lanarkite. Crystals are also produced by in situ oxidation in the vein. It is often associated with its polymorphs susannite and macphersonite, and sometimes occurs with scotlandite Pb(S4+O3), native silver or caledonite.
At Silver Gill it occurs associated with anglesite and caledonite.
At Driggith Mine dumps it occurs in oxidised galena-bearing fragments associated with caledonite, anglesite and cerussite.
At the Brae Fell Mine it occurs associated with anglesite, caledonite, cerussite and linarite.

Heating leadhillite causes it to reversibly transform into its polymorph susannite in the temperature range from 50 to 82°C

Lepidocrocite

Formula: Fe3+O(OH)
Dimorphous with goethite.
Specific gravity: 4.05 to 4.13
Hardness: 5
Streak: Orange
Colour: Deep red, red-brown
Environments:

Sedimentary environments

Lepidocrocite is common in iron ore deposits.
Common impurities: Mn

Lepidolite

Lepidolite is a series between polylithionite and trilithionite Formula:
Polylithionite: KLi2AlSi4O10F2
Trilithionite: KLi1.5Al1.5(Si3Al)O10F2
Both are phyllosilicates (sheet silicates) mica group
Specific gravity: 2.8 to 2.9
Hardness: 2 to 2½
Streak: White
Colour: Pink, lilac, reddish; The lavender pink colour is due to Mn3+. The colour of the mineral is not an indication of its lithium content.
Solubility: Slightly soluble in hydrochloric acid
Environments:

Pegmatites
Hydrothermal environments

Lepidolite is a comparatively rare mineral, found in lithium-rich pegmatites, usually associated with other lithium-bearing minerals such as pink and green tourmaline, amblygonite and spodumene, as well as microcline and quartz. It is often intergrown with muscovite in parallel layers. It appears that lepidolite forms late in the crystallisation of pegmatites, succeeding the more common muscovite and biotite of the outer pegmatite zones.
It may also be found in high temperature veins.

Common impurities: Polylithionite: Ti,Fe,Mn,Mg,Ca,Na,H2O

Leucite

Formula: K(AlSi2O6)
Tectosilicate (framework silicate), feldspathoid
Specific gravity: 2.45 to 2.5
Hardness: 5½ to 6
Streak: White
Colour: White, colourless
Solubility: Slightly soluble in hydrochloric acid
Environments:

Plutonic igneous environments (rarely)
Volcanic igneous environments
Hydrothermal environments

Leucite is very rare in plutonic masses. In volcanic environments leucite is characteristic of potassium-rich mafic and ultramafic lavas, where it forms directly from cooling lava in low silica environments with high potassium content.
Leucite is a primary rock-forming mineral.
It may be found in andesite, basalt, diorite, gabbro, syenite and trachyte.
If sodium is abundant, nepheline occurs rather than leucite.
Leucite never occurs together with quartz; it reacts with free quartz to form K-feldspar.
In the oxidation zone it often transforms to pseudoleucite, which is a mixture of nepheline and orthoclase; further oxidation may break it down into kaolinite or clay.
In pre-tertiary rocks (older than 65 million years) leucite readily decomposes to zeolites, analcime and other secondary minerals.
At the Nyiragongo volcano, Congo, leucite is associated with pyroxene, olivine and magnetite.

Common impurities: Ti,Fe,Mg,Ca,Ba,Na,Rb,Cs,H2O

Leucophanite

Formula: NaCaBeSi2O6F
Sorosilicate
Specific gravity: 2.96
Hardness: 3 to 4
Streak: White
Colour: Colourless, pale yellow, light green
Environments:

Pegmatites

Leucophanite occurs in nepheline-syenite pegmatites associated with pyrochlore, nepheline, mosandrite-(Ce), albite, aegirine, orthoclase, natrolite, analcime, serandite, polylithionite, ancylite, astrophyllite, catapleiite, epididymite, rhodochrosite and fluorite.

Common impurities: Al,Fe,Mg,K,H2O

Lévyne

Formula: (Ca,Na2)3(Si12Al6)O36.18H2O tectosilicate (framework silicate), zeolite group
Specific gravity: 2.09 to 2.16
Hardness: 4 to 4½
Streak: White
Colour: Colourless, white, grey, yellow, red
Environments:

Basaltic cavities

Lévyne occurs most commonly in cavities in low silica volcanic rocks such as olivine basalt, and rarely in andesite, often associated with other zeolites, especially offretite and erionite.

Limonite

"Limonite" is a term for unidentified massive hydroxides and oxides of iron, with no visible crystals, and a yellow-brown streak. It is most commonly the mineral species goethite, but it can also consist of varying proportions of other minerals, including jarosite group minerals and hematite.

Linarite

Formula: CuPb(SO4)(OH)2 sulphate
Specific gravity: 5.3 to 5.5
Hardness: 2½
Streak: Light blue
Colour: Blue
Solubility: Moderately soluble in nitric acid
Environments:

Hydrothermal environments

Linarite occurs as a secondary mineral in the oxidation zone of high temperature hydrothermal deposits, where it is formed as an alteration product of galena. In some Cumbrian localities it is found on limonitic quartz or partly decomposed galena with cerussite. It also occurs near the contact between galena and the surrounding matrix, if any copper sulphides are present. It may be formed by post-mining oxidation. The linarite/a>, anglesite, brochantite assemblage is typical for some localities, and helps to distinguish linarite from azurite.
Linarite has been found pseudomorphed by chrysocolla, malachite and brochantite, and it is often intergrown with leadhillite.

Lizardite

Formula: Mg3Si2O5(OH)4 phyllosilicate (sheet silicate), serpentine group
Specific gravity: 2.55 to 2.60
Hardness: 2½
Streak: White
Colour: Green, green blue, yellow, white.
Environment

Metamorphic environments

Lizardite is formed by the alteration of magnesium silicates below 75oC

Alteration

See results for serpentine, which is a group of minerals including serpentine, chrysotile and lizardite, all of which share the same formula, although they have slightly different structures.

Lindqvistite

Formula: Pb2Mn2+Fe3+16O27
Multiple oxide
Specific gravity: 5.76
Hardness: 6
Streak: Brownish black
Colour: Black
Solubility: Slowly soluble in cold hydrochloric acid, insoluble in nitric or sulphuric acid
Environment

Metamorphic environments

Lindqvistite occurs in a regionally metamorphosed lead-bearing Fe-Mn skarn deposit, hosted in dolomitic marble, associated with hematite, jacobsite, plumboferrite, andradite, phlogopite, calcite, hedyphane, baryte, copper, cuprite, malachite and azurite.

Common impurities: Zn,Al,Ti,Si

Liroconite

Formula: Cu2Al(AsO4)(OH)4.4H2O
Hydrated arsenate containing hydroxyl
Specific gravity: 2.9
Hardness: 2 to 2½
Streak: Light blue
Colour: Sky-blue to green
Solubility: Soluble in acids
Environment

Hydrothermal environments

Liroconite is a rare secondary mineral found in oxidised zones of copper deposits, associate with olivenite, chalcophyllite, clinoclase, cornwallite, strashimirite, malachite, cuprite and “limonite".

At Cerro Gordo mine, Inyo county, California, USA, liroconite occurs with linarite and caledonite.

At the type locality, Wheal Gorland, Cornwall, England, liroconite occurs with cornubite and cornwallite.

At Wheal Unity, Cornwall, England liroconite has been found on cuprite associated with malachite, azurite and clinoclase.

Common impurities: P

Litharge

Formula: PbO simple oxide
Specific gravity: 9.14
Hardness: 2
Streak: Red
Colour: Red
Solubility: Litharge is easily fusible, and soluble in hydrochloric and nitric acid. Slowly soluble in alkalis.
Environment

Metamorphic environments
Hydrothermal environments

Litharge occurs as alteration crusts on massicot, with the change occurring at 488oC, and by alteration of other lead-bearing minerals

Luddenite

Formula: Cu2Pb2Si5O14.14H2O
Unclassified silicate
Specific gravity: 4.45
Hardness: 4
Streak: Pale nickel green
Colour: Green
Solubility: Luddenite is not easily soluble in acids. Dissolution even in heated 50% HNO3 is slow. It readily fuses to a runny lemon yellow slag in the closed tube.
Environments:

Hydrothermal environments

Luddenite occurs in thoroughly oxidised lead-copper sulphide ores, associated with galena, chalcopyrite, fluorite, quartz, alamosite, melanotekite cerussite, chalcocite, shattuckite, chrysocolla and wickenburgite.

At the type locality, an unnamed prospect near Artillery Peak, Mohave county, Arizona, USA, luddenite occurs with galena, chalcopyrite, fluorite, alamosite, melanotekite and hyalotekite.

Common impurities: Ti

Macfallite

Formula: Ca2Mn3+3(SiO4)(Si2O7)(OH)3
Sorosilicate
Specific gravity: 3.43
Hardness: 5
Streak: Brown with reddish tint
Colour: Brown to reddish brown, maroon
Environments:

Metamorphic environments
Basaltic cavities

At Manganese lake, Keweenaw county, Michigan, USA, macfallite occurs in basalt associated with manganite, braunite, orientite and pyrolusite. The assemblage replaces calcite in fissures and lenses in the basalt, and most of the crystals are coated with late-stage calcite. Macfallite also occurs with pumpellyite, and these two mineral appear to have formed at the same time.

At Faggiona, Italy, macfallite replaces braunite under low-temperature metamorphic conditions associated with braunite, quartz and manganoan richterite.

Common impurities: Ti,Al,Fe,Cr,V,Cu,Mg,K,Na,H2O

Magnesioferrite

Formula: MgFe3+2O4
Multiple oxide, spinel group, magnesioferrite-magnetite series
Specific gravity: 4.6
Hardness: 6 to 6½
Streak: Black or dark red
Colour: Black, reddish-brown in transmitted light
Environments:

Metamorphic environments

Magnesioferrite is most commonly found in fumeroles where it probably formed by the reaction at high temperature of steam and ferric chloride with magnesian material . It is also found in sanidinite facies combustion-metamorphosed marl and burning coal heaps, and in metamorphosed dolostone. It is an accessory mineral in some kimberlite, gabbro and carbonatites.
Magnesioferrite is associated with hematite, titanium-rich magnetite, iron-rich diopside and dolomite, and at Långban, Sweden, occasionally with bromellite.

Magnesite

Formula: Mg(CO3) carbonate
Specific gravity: 2.98 to 3.02
Hardness: 3½ to 4½
Streak: White
Colour: Colourless, white, greyish-white, yellowish, brown, faintly pink, lilac-rose; colourless in transmitted light
Solubility: Readily soluble in hydrochloric, sulphuric and nitric acids. Slightly affected by cold acids. Readily soluble in warm hydrochloric acid with effervescence. Slightly soluble in water with the solubility increasing with the presence of NaCl, Na2SO4, or CO2
Environments:

Sedimentary environments

Magnesite is an evaporite mineral that may be associated with serpentine.

Alteration

antigorite and magnesite to forsterite, CO2 and H2O
Mg3Si2O5(OH)4 + MgCO3 → 2Mg2SiO4 + CO2 + 2H2O

forsterite and CO2 to enstatite and magnesite
Mg2SiO4 + CO2 ⇌ MgSiO3 + MgCO3

magnesite and H2O to hydromagnesite Mg5(CO3)4(OH)2.4H2O and CO2
5MgCO3 + 5H2O → Mg5(CO3)4(OH)2.4H2O + CO2
Magnesite may react with water to form hydromagnesite or other low-temperature hydrated carbonates.

olivine and CO2 to enstatite- ferrosilite and magnesite- siderite
(Mg,Fe)2SiO4 + CO2 → (Mg,Fe2+)SiO3 + (Mg,Fe)CO3

serpentine (chrysotile) and CO2 to talc, magnesite and H2O
2Mg3Si2O5(OH)4 + 3CO2 → Mg3Si4O10(OH)2 + 3MgCO3 + 3H2O
Serpentine (chrysotile) is not stable in the presence of carbon dioxide and reacts with it according to the above equation.

Common impurities: Fe,Mn,Ca,Co,Ni,ORG

Localities

Brazil

There is a magnesite mine in Brumado, Bahia, where the rare halide sellaite occurs in vugs associated with magnesite and quartz.

Magnetite

Formula: Fe2+Fe3+2O4 multiple oxide, spinel group
Specific gravity: 5.175
Hardness: 5½ to 6½
Streak: Black
Colour: Black
Solubility: Slightly soluble in hydrochloric acid
Environments:

Plutonic igneous environments
Volcanic igneous environments
Carbonatites
Sedimentary environments
Placer deposits
Metamorphic environments (typical)
Hydrothermal environments

Magnetite is a primary and secondary mineral found in igneous environments, carbonatites, sedimentary environments including placers, regional metamorphic environments, massive hydrothermal replacement deposits and hydrothermal replacement lodes. It is a common constituent of sedimentary and metamorphic banded iron formations, and in such occurrences it is of a chemical sedimentary origin. It is found in black sands often associated with corundum, forming emery. In metamorphic environments it may be associated with serpentine. In some rocks magnetite may be one of the chief constituents and form large ore bodies.
It may be found in andesite, basalt, gabbro, granite, kimberlite, rhyolite, syenite,

Alteration

aenigmatite, anorthite and O2 to hedenbergite, albite, ilmenite and magnetite
½Na4[Fe2+10Ti2]O4[Si12O36] + CaAl2Si2O8 + ½O2 = CaFe2+Si2O6 + 2NaAlSi3O8 + Fe2+Ti4+O3 + Fe2+Fe3+2O4

albite, diopside and magnetite to aegirine, Si2O6, garnet and quartz
2Na(AlSi3O8) + CaMgSi2O6 + Fe2+Fe3+2O4 ⇌ 2NaFe3+Si2O6 + Si2O6 + CaMgFe2+Al2(SiO4)3 + SiO2
This reaction may occur in blueschist facies rocks in Japan.

fayalite and H2O to magnetite, SiO2 and H2
3Fe2+2(SiO4) + 2H2O &38594; Fe2+Fe3+2O4 + 3SiO2 + 2H2
This reaction is highly exothermic

fayalite, H2O and O2 to cronstedtite and magnetite
6Fe2+2(SiO4) + 6H2O + ½O2 = 3Fe3Si2O5(OH)4 + Fe2+Fe3+2O4

forsterite, fayalite, H2O and CO2 to serpentine, magnetite and methane
18 Mg2SiO4 + 6Fe2SiO4 + 26H2O + CO2 → 12Mg3Si2O5(OH)4 + 4Fe3O4 + CH4

hematite, wüstite, quartz and calcite to andradite, hedenbergite, magnetite and CO2
2Fe2O3 + 2FeO + 5SiO2 + 4CaCO3 → Ca3Fe3+2(SiO4)3 + CaFe2+Si2O6 +Fe2+Fe3+2O4 +4CO2
If wüstite, FeO, is also introduced hedenbergite and magnetite may form in addition to andradite:

titanomagnetite (ilmenite combined with magnetite), quartz, and aegirine-hedenbergite to aenigmatite, hedenbergite, magnetite and O2
6(Fe2+Ti4+O3 + Fe2+Fe3+2O4) + 12SiO2 + 12(NaFe3+Si2O6 + CaFe2+Si2O6) ⇌ 3Na4[Fe2+10Ti2]O4[Si12O36] + 12CaFe2+Si2O6 + 2Fe2+Fe3+2O4 + 5O2

jadeite, diopside, magnetite and quartz to aegirine, kushiroite (pyroxene) and hypersthene
2NaAlSi2O6 + CaMgSi2O6 + Fe2+Fe3+2O4 + SiO2 ⇌ 2NaFe3+Si2O6 + CaAlAlSiO6 + MgFeSi2O6
Aegirine in blueschist facies rocks may be formed by the above reaction.

magnetite to hematite
Magnetite may convert to hematite, and vice versa, depending on the pressure and temperature, according to the equation:
magnetite + oxygen ⇌ hematite
2Fe3O4 + ½O2 ⇌ 3Fe2O3

olivine and H2O to serpentine, magnetite and H2
6(Mg1.5Fe0.5)SiO4 + 7H2O → 3Mg3Si2O5(OH)4 + Fe2+Fe3+2O4 + H2
The iron Fe in olivine does not enter into the serpentine, but recrystallises as magnetite.

staurolite, annite and O2 to hercynite, magnetite, muscovite,corundum, SiO2 and H2O
2Fe2+2Al9Si4O23(OH) + KFe2+3 (AlSi3O10)(OH)2 +2O2 → 4Fe2+Al2O4 + Fe2+Fe3+2O4 + KAl2 (AlSi3O10)OH)2 + 4Al2O3 + 8SiO2 + 2H2O

Common impurities: Mg,Zn,Mn,Ni,Cr,Ti,V,Al

Magnetoplumbite

Formula: PbFe3+12O19 multiple oxide
Specific gravity: 5.52
Hardness: 6
Streak: Dark brown
Colour: Grey-black
Solubility: Slowly soluble in hydrochloric acid with slight evolution of Cl2
Environments:

Metamorphic environments

Magnetoplumbite occurs in skarn associated with metamorphosed Fe-Mn orebodies, associated with hematite, jacobsite, hedyphane, braunite, manganoan phlogopite, calcite, andradite and celsian.

Magnussonite

Formula: Mn2+10As3+6O18(OH,Cl)2
Arsenite containing hydroxyl and/or halogen
Specific gravity: Greater than 4.4
Hardness: 3½ to 4
Streak: White
Colour: Grass reen to emerald green
Environments:

Metamorphic environments

Magnussonite occurs in a metamorphosed Fe-Mn orebody.
At the type locality, Långban, Filipstad, Värmland, Sweden, magnussonite occurs as fine-grained encrustations in fissures in dolomite impregnated with hausmannite or in fine-grained hematite, associated with trigonite, dixenite, calcite, dolomite, hausmannite, hematite and manganiferous serpentine.
At the Brattfors mine, Sweden, magnussonite is associated with katoptrite, sonolite, hausmannite, manganosite and magnetite.
At Sterling Hill, New Jersey, USA, magnussonite occurs very rarely in a metamorphosed stratiform zinc orebody, associated with zincite, willemite, franklinite and kraisslite.

Malachite

Formula: Cu2(CO3)(OH)2 anhydrous carbonate containing hydroxyl
Specific gravity: 3.6 to 4.05
Hardness: 3½ to 4
Streak: Green
Colour: Green
Solubility: Readily soluble in hydrochloric, sulphuric and nitric acid
Environments:

Carbonatites
Hydrothermal environments

Malachite is a very common secondary copper mineral found in the oxidation zones of high temperature hydrothermal copper deposits, often in limestone, associated with azurite, cuprite, native copper, and iron oxides.

Alteration

azurite and H2O to malachite and CO2
2Cu3(CO3)2(OH)2 + H2O → 3Cu2(CO3(OH)2 + CO2
Azurite is unstable under atmospheric conditions, and slowly converts to the more stable malachite according to the above reaction. This instability is evidenced by the existence of many pseudomorphs of malachite after azurite; pseudomorphs of azurite after malachite are extremely rare.

Common impurities: Zn,Co,Ni

Manganhumite

Formula: Mn2+7(SiO4)3(OH)2
Nesosilicate (insular SiO4 groups), humite group
Specific gravity: 3.83
Hardness: 4
Streak: Yellow-brown
Colour: Pale to deep brownish orange, medium brown
Solubility: Easily soluble in warm diluted hydrochloric acid, leaving a silica gel
Environments:

Metamorphic environments

At Brattforsmine,Sweden, manganhumite is a late-stage skarn mineral formed in recrystallized limestone banded between layers of manganese ore minerals, associated with katoptrite, magnetite, manganostibite, magnussonite, tephroite, galaxite and manganosite.
At BaldKnob, NorthCarolina, USA, manganhumite occurs in a manganese deposit metamorphosed to the amphibolite facies, associated with sonolite, alleghanyite, rhodonite, kutnohorite, galaxite, jacobsite, kellyite and alabandite.

Alteration:

manganhumite and H2O to alleghanyite and SiO2
5Mn7(OH)2(SiO4)3 + 2H2O ⇌ 7Mn5(OH)2(SiO4)2 + SiO2

Common impurities: Ti,Al,Fe,Ca,F,H20,P

Manganite

Formula: Mn3+O(OH) oxide containing hydroxyl
Specific gravity: 4.3 to 4.4
Hardness: 4
Streak:
Colour: Brownish black to black
Solubility: Slightly soluble in hydrochloric acid; moderately soluble in sulphuric acid
Environments:

Pegmatites
Hydrothermal environments

Manganite is found associated with other manganese oxides in deposits formed by meteoric waters. It is often found in epithermal (low temperature) hydrothermal veins associated with acanthite, baryte, cinnabar, pyrolusite, quartz, siderite and calcite.

It frequently alters to pyrolusite.

Manganosite

Formula: MnO simple oxide, periclase group
Specific gravity: 5.364
Hardness: 5½
Streak: Brown
Colour: Emerald-green, darkening on exposure to black
Solubility: Dissolves with difficulty in strong hydrochloric or nitric acid to a colourless solution
Environments:

Metamorphic environments

Manganosite occurs in metamorphosed manganese deposits as an alteration product of rhodochrosite or other manganese minerals, formed during oxygen-deficient metamorphism of manganese-bearing deposits. It also occurs in marine manganese nodules.

Alteration

manganosite and O2 to hausmannite
6MnO + O2 ⇌ 2Mn2+Mn3+2O4
A higher temperature favours the reverse reaction

manganosite and quartz to rhodonite
MnO + SiO2 ⇌ Mn2+SiO3

manganosite and quartz to tephroite
2MnO + SiO2 ⇌ Mn2+2SiO4

manganosite and rhodonite to tephroite
MnO + Mn2+SiO3 ⇌ Mn2+2SiO4

rhodochrosite to manganosite and CO2
MnCO3 ⇌ MnO + CO2
Higher temperature favours the forward reaction

Localities

Sweden

At Långban, Sweden, manganosite is associated with pyrochroite, manganite and dolomite.

At Nordmark, Sweden, manganosite is associated with pyrochroite, hausmannite, periclase, garnet and dolomite

USA

At Franklin, New Jersey, USA, manganosite is associated with franklinite, willemite, calcite and zincite

Mansfieldite

Formula: Al(AsO4).2H2O
Forms a series with scorodite.
Specific gravity: 3.03
Hardness: 3½ to 4
Streak: White
Colour: White, light gray; colourless in transmitted light.
Environments:

Hydrothermal environments

At the type locality, Hobart Butte, Oregon, USA, mansfieldite is associated with scorodite, realgar and kaolinite.

Marcasite

Formula: FeS2 sulphide
Specific gravity: 4.887
Hardness: 6 to 6½
Streak: Dark grey to black
Colour: Pale brass-yellow, tin-white on fresh exposures.
Solubility: Insoluble in hydrochloric acid and sulphuric acid
Environments:

Sedimentary environments
Metamorphic environments
Hydrothermal environments

Marcasite most frequently occurs as replacement deposits also often in concretions and in limestone, and often in concretions and replacing organic matter and forming fossils in sedimentary beds, particularly coal beds. It is also found in chemical sedimentary environments, massive and disseminated hydrothermal replacement deposits and hydrothermal replacement lodes and in epithermal (low temperature) hydrothermal veins.
Marcasite may be found in clay, marl, shale and dolostone.
In hydrothermal veins it may be associated with pyrite.

Alteration

Marcasite is a mineral of low-temperature, near-surface, environments, forming from acid solutions. Pyrite, the more stable form of FeS2, forms in higher temperatures and lower acidity or alkaline environments.

Common impurities: Cu,As

Margarite

Formula: CaAl2(Al2Si2O10)(OH)2 phyllosilicate (sheet silicate), mica group
Forms a solid solution series with paragonite
Specific gravity: 3.0 to 3.1
Hardness: 3½ to 4½ on {001}, 6 perpendicular to {001}
Streak: White
Colour: Greyish, pale pink, yellow, green. Colourless in thin section.
Solubility: Only partially decomposed by boiling acids
Environments:

Pegmatites
Metamorphic environments

Margarite occurs typically in low to medium grade metamorphic deposits as an alteration product of corundum, also in chlorite and mica schist with staurolite and schorl. It is typically associated with corundum, also diaspore, tourmaline, staurolite, glaucophane, chlorite, manganite, spinel, andalusite, calcite and quartz. It is a mineral of the blueschist, prehnite-pumpellyite, greenschist and amphibolite facies.

Alteration

kyanite and zoisite to margarite and anorthite
2Al2O(SiO4) + 2Ca2Al3[Si2O7][SiO4]O(OH) ⇌ CaAl2(Al2Si2O10)(OH)2 + Ca(Al2Si2O8)
The equilibrium temperature for this reaction at 6 kbar pressure is about 520oC (amphibolite facies), and at 9 kbar it is about 675oC (amphibolite facies). At any pressure the equilibrium is displaced to the right at higher temperatures, and to the left at lower temperatures.

lawsonite to zoisite, margarite, quartz and H2O
5CaAl2(Si2O7)(OH)2.H2 ⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + CaAl2(Al2Si2O10)(OH)2 + 2SiO2 + 8H2O
The equilibrium temperature for this reaction at 6.5 kbar pressure is about 425oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and diaspore to margarite and H2O
CaAl2(Si2O7)(OH)2.H2O + 2AlO(OH) ⇌ CaAl2(Al2Si2O10)(OH)2 + 2H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 460oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and kaolinite to margarite, pyrophyllite and H2O
CaAl2(Si2O7)(OH)2.H2 + 2Al2Si2O5(OH)4 ⇌ CaAl2(Al2Si2O10)(OH)2 + Al2Si4O10(OH)2 + 4H2O
The equilibrium temperature for this reaction at 5 kbar pressure is about 360oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and kaolinite to margarite, quartz and H2O
CaAl2(Si2O7)(OH)2.H2 + Al2Si2O5(OH)4 ⇌ CaAl2(Al2Si2O10)(OH)2 + 2SiO2 +3H2O
The equilibrium temperature for this reaction at 2 kbar pressure is about 300oC (prehnite-pumpellyite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and kyanite to margarite, pyrophyllite and H2O
3CaAl2(Si2O7)(OH)2.H2 + 4Al2OSiO4 ⇌ 3CaAl2(Al2Si2O10)(OH)2 + Al2Si4O10(OH)2 + 2H2O
The equilibrium temperature for this reaction at 6.5 kbar pressure is about 390oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and kyanite to margarite, quartz and H2O
CaAl2(Si2O7)(OH)2.H2 + Al2OSiO4 ⇌ CaAl2(Al2Si2O10)(OH)2 + SiO2 + H2O
The equilibrium temperature for this reaction at 8 kbar pressure is about 450oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

lawsonite and margarite to zoisite, kyanite and H2O
3CaAl2(Si2O7)(OH)2.H2 + CaAl2(Al2Si2O10)(OH)2 ⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + 2Al2OSiO4 + 6H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 500oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite to corundum, anorthite and H2O
CaAl2(Al2Si2O10)(OH)2 ⇌ Al2O3 + Ca(Al2Si2O8)
The equilibrium temperature for this reaction at 6 kbar pressure is about 610oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite to corundum, zoisite, kyanite and H2O
4CaAl2(Al2Si2O10)(OH)2 ⇌ 3Al2O3 + 2Ca2Al3[Si2O7][SiO4]O(OH) + 2Al2OSiO4 + 3H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 650oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite and quartz to anorthite, andalusite and H2O
CaAl2(Al2Si2O10)(OH)2 + SiO2 ⇌ Ca(Al2Si2O8) + Al2OSiO4 + H2O
The equilibrium temperature for this reaction at 2 kbar pressure is about 440oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite and quartz to anorthite, kyanite and H2O
CaAl2(Al2Si2O10)(OH)2 + SiO2 ⇌ Ca(Al2Si2O8) + Al2OSiO4 + H2O
The equilibrium temperature for this reaction at 5 kbar pressure is about 520oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

margarite and quartz to zoisite, kyanite and H2O
4CaAl2(Al2Si2O10)(OH)2 + 3SiO2 ⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + 5Al2OSiO4 + 3H2O
The equilibrium temperature for this reaction at 8 kbar pressure is about 510oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

zoisite, kyanite and diaspore to margarite
Ca2Al3[Si2O7][SiO4]O(OH) + Al2OSiO4 + 3AlO(OH) ⇌ 2CaAl2(Al2Si2O10)(OH)2
The equilibrium temperature for this reaction at 12 kbar pressure is about 480oC (blueschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

zoisite, margarite and quartz to anorthite and H2O
2Ca2Al3[Si2O7][SiO4]O(OH) + CaAl2(Al2Si2O10)(OH)2 + 2SiO2 ⇌ 5Ca(Al2Si2O8) + 2H2O
The equilibrium temperature for this reaction at 6 kbar pressure is about 540oC (amphibolite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

Common impurities: Na,Mg,Cr,Li,Mn,Fe,K,Ba,Sr,H2O

Localities

Australia

Gibralta, Western Australia: Margarite occurs embedded in corundum.

Russia

Mount Yatyrgvata, northern Caucasus, Russia: Sodian margarite occurs at a pegmatite- amphibolite intrusion boundary.

UK

Near Ferrercairn village, Glen Esk, Scotland: Margarite occurs as pseudomorphs after kyanite and contains considerable paragonite in solid solution.

USA

Near Meadow Valley, Plumas County, California, USA: Margarite occurs with corundum.

Emery mines, Chester, Hampden County, Massachusetts, USA: Margarite occurs with corundum, magnetite and diaspore.

Massicot

Formula: PbO simple oxide, dimorph of litharge
Specific gravity: 9.56
Hardness: 2
Streak: yellow
Colour: Yellow, sometimes with a reddish tint. Nearly colourless to pale yellow in transmitted light.
Environments:

Hydrothermal environments
Volcanic sublimates

Massicot is a rare mineral of secondary origin associated with galena and dimorphous with litharge. It may be an oxidation product of galena, bournonite, boulangerite or other lead-bearing minerals and it is also found as a sublimation product in fumeroles. It is associated with cerussite, litharge, minium, wulfenite, antimony oxides and limonite.

Mawbyite

Formula: PbFe3+2(AsO4)2(OH)2
Specific gravity: 5.53 (calculated)
Hardness: 4
Streak: Orange-yellow
Colour: Orange-brown, red-brown
Environments:

Hydrothermal environments

The formation of mawbyite is probably related to the pH of circulating waters in the oxidation zone.
At Kintore, New South Wales, Australia, mawbyite occurs in the oxidised zone on spessartine quartz rocks in an arsenic-rich reaction halo associated with members of the corkite-beudantite series, adamite, olivine, duftite, mimetite, bayldonite, hidalgoite and pharmacosiderite.

Mazzite

Mazzite is the name for two minerals
Mazzite-Mg: Mg5(Si26Al10)O72.30H2O
Mazzite-Na: Na8(Si28Al8)O72.30H2O
Tectosilicates (framework silicates), zeolite group
Specific gravity: 2.11
Streak: White
Colour: Colourless
Environments:

Volcanic igneous environments
Hydrothermal environments

Mazzite occurs in basalt associated with phillipsite, chabazite and offretite. It is of hydrothermal origin.

Melanotekite

Formula: Pb2Fe3+2O2(Si2O7) sorosilicate (Si2O7 groups)
Specific gravity: 5.73 to 6.19
Hardness: 6½
Streak: Greenish
Colour: Grey, black
Solubility: Decomposed by nitric acid
Environments:

Pegmatites
Metamorphic environments

Melanotekite occurs with native lead at the type locality, Långban, Sweden, in a pre-Cambrian metamorphosed Fe-Mn deposit. At Artillery Peaks, Arizona, USA it is found in oxidised Pb-Cu ores, and at Dara-i-Pioz, Tajikistan, it occurs in an aluminium-poor, sodium and potassium-rich pegmatite.
At 650oC, melanotekite can coexist with quartz, hematite, magnetoplumbite and plumboferrite.
Common impurities: Ti,Al,Mn,Mg

Melanterite

Formula: Fe(SO4).7H2O sulphate
Specific gravity: 1.89
Hardness: 2
Streak: White
Colour: Colourless to white or green, also greenish-blue to blue with increased Cu content; colourless to pale green in transmitted light. Usually a yellowish-white after exposure to air and moisture.
Solubility: Readily soluble in water
Environments:

hydrothermal environments

Alteration

Melanterite is a secondary mineral formed by the oxidation of pyrite, marcasite and other iron sulphides in massive hydrothermal replacement deposits. It is often found in mines as a post-mining formation.
Melanterite may dehydrate to siderotil.

pyrite (primary) O and H2O to secondary melanterite and sulphuric acid.
FeS2 + 7O + 8H2O → FeSO4.7H2O + H2SO4
Melanterite indicates the presence of sulphuric acid, and it should be handled with care.

Common impurities: Cu,Mg

Melilite

Melilite is a group of tetragonal sorosilicates (Si2O7 groups). The most abundant members of the group are minerals in the åkermanite-gehlenite series
Formulae
Åkermanite: Ca2MgSi2O7
Gehlenite: Ca2Al(SiAl)O7
Melilite is a common component of magnesian skarn, and it also may be found in granite. It has been reported in a lamprophyre dike at Cripple Creek, Colorado, USA.
Quartz never occurs with melilite.

Alteration

nepheline and diopside to melilite, forsterite and albite
3NaAlSiO4 + 8CaMgSi2O6 ⇌ 4Ca2MgSi2O7 + 2Mg2SiO4 + 3NaAlSi3O8
This reaction is in equilibrium at about 1180oC, with lower temperatures favouring the forward reaction.

Mendipite

Formula: Pb3O2Cl2 oxyhalide
Specific gravity: 7.24
Hardness: 2½ to 3
Streak: White
Colour: Colourless, white, grey, often tinged yellow, blue, red; nearly colourless in transmitted light
Solubility: Soluble in dilute nitric acid
Environments:

Sedimentary environments

The Mendips is a range of limestone hills, mostly in Somerset, England. This is the type locality for mendipite, which is one of the signature minerals of the manganese deposits there. Mendipite forms only when the supply of CO2 is restricted; if it is not, cerussite forms instead. This is why mendipite can only be found in the sealed environment of a cavity in the manganese oxides, isolated from the surrounding limestone which otherwise would be a source of abundant CO2.

Merlinoite

Formula: K5Ca2(Si23Al9)O64.24H2O tectosilicate (framework silicate), zeolite group
Specific gravity: 2.14 to 2.27
Hardness: 4½
Streak: White
Colour: Colourless to white
Environments:

Volcanic igneous environments
Pegmatites
Sedimentary environments
Basaltic cavities

Merlinoite is a secondary mineral occuring in cavities in basalt, in pegmatites, in pyroxene-rich volcanic ejecta, and as a diagenetic alteration in volcanic ash falls.
Common impurities: Fe

Merwinite

Formula: Ca3Mg(SiO4)2 nesosilicate (insular SiO4 groups)
Specific gravity: 3.15 to 3.32
Hardness: 6
Streak: White
Colour: White, colourless, light green, light gray green

Metamorphic environments

At the type locality merwinite is found in high temperature, low pressure contact metamorphic zones with marbles; in siliceous dolomitic limestone in contact metamorphic zones, it is formed at relatively elevated temperatures.

Alteration

monticellite and spurrite to merwinite and calcite
2CaMg(SiO4) + Ca5(SiO4)2(CO3) ⇌ 2Ca3Mg(SiO4)2 + CaCO3

monticellite, spurrite and quartz to merwinite and CO2
5CaMg(SiO4) + Ca5(SiO4)2(CO3) + SiO2 ⇌ 5Ca3Mg(SiO4)2 + 2CO2

Common impurities: Al, Fe

Mesolite

Formula: Na2Ca2(Si9Al6)O30.8H2O tectosilicate (framework silicate) zeolite group
Specific gravity: 2.26
Hardness: 5
Streak: White
Colour: Colourless, white, gray, yellowish

Hydrothermal environments
Basaltic cavities

Mesolite commonly occurs in cavities in volcanic rocks, typically basalt, also in andesite, porphyry (rock with coarse phenocrysts in a finer groundmass) and hydrothermal veins. In basaltic cavities it is generally in association with other zeolites.

In the vicinity of Meshkinshahr, Ardabil Province, Iran, mesolite is the most common zeolite, almost always associated with thomsonite and analcime.

In basaltic cavities in Oregon, USA, mesolite is associated with calcite, chabazite, analcime and stilbite.

Common impurity: K

Metatorbernite

Formula:Cu(UO2)2(PO4)2.8H2O hydrated normal phosphate
The prefix "meta" denotes a dehydration product (of torbernite)
Specific gravity: 3.52 to 3.70
Hardness: 2½
Streak: Pale green
Colour: Pale green to dark green
Solubility: Moderately soluble in hydrochloric, sulphuric and nitric acids

Igeous environments
Hydrothermal environments

Metatorbernite is typically a secondary mineral, formed as a dehydration product of torbernite, which is unstable; it also may be formed directly above 75oC.

Common impurities: Ca,Ba,Mg

Metavariscite

Formula: Al(PO4).2H2O hydrated normal phosphate, variscite group, dimorph of variscite
Specific gravity: 2.54
Hardness: 3½
Streak: White
Colour: Light green; colourless in transmitted light

Environments:

Hydrothermal environments

Metavariscite occurs in cavities in variscite nodules at the type locality, Edison-Bird Mine, Utah, USA, and in phosphatised andesite at the Pacific Ocean island of Malpelo (Colombia).

Mica

The mica group is a group of sheet silicates, including muscovite and biotite.
Mica is a common constituent of most pegmatites, granite, diorite, gabbro, andesite and gneiss.
It also may be found in quartzolite, kimberlite, clay, skarn, amphibolite and eclogite.
It is never found in the granulite facies rocks.

Microcline

Formula: K(AlSi3O8) tectosilicate (framework silicate)
Microcline is a K-feldspar.
Amazonite is a variety of microcline
Adularia is a more ordered low-temperature variety of orthoclase or partially disordered microcline.
Hyalophane is a barium-rich variety of microcline or orthoclase.
Properties of microcline:
Specific gravity: 2.54 to 2.57
Hardness: 6 to 6½
Streak: White
Colour: White, blue, green, pink, yellow
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments (microcline):

Pegmatites
Sedimentary environments
Metamorphic environments

Microcline occurs mainly as a primary mineral in schist and gneiss. K-feldspars are essential constituents of granite, and microcline is the common K-feldspar of pegmatites. In sedimentary rocks microcline is present in feldspar-rich sandstone.
Microcline is characteristic of the granulite facies and it is also a mineral of the albite-epidote-hornfels, hornblende-hornfels and pyroxene-hornfels facies.

At Broken Hill, New South Wales, Australia, microcline variety hyalophane has been described from lenses and streaks in acid gneiss.
At the Kaso mine, Japan, microcline variety hyalophane occurs in veins with manganese-rich tremolite, rhodonite, rhodochrosite and spessartine.
In the manganese ores of Otjosondu, Namibia, hyalophane is found in a rock consisting mainly of the manganese-rich garnet calderite, and it also occurs as small veinlets in the garnet.
At Slyudyanka, Siberia, Russia, microcline variety hyalophane occurs in phlogopite-calcite veins in a pyroxene-amphibole gneiss.

Alteration

phlogopite, calcite and quartz to diopside, microcline, H2O and CO2
KMg3(AlSi3O10)(OH)2 + 3CaCO3 + 6SiO2 = 3CaMgSi2O6 + K(AlSi3O8) + H2O + 3CO2
In reaction zones between interbedded carbonate and pelitic beds of the calc-mica schists, phlogopite may alter according to the above reaction.

Common impurities in microcline: Fe,Ca,Na,Li,Cs,Rb,H2O,Pb

Microlite

Microlite is a group of minerals Formula: (Na,Ca)2Ta2O6(O,OH,F)
Specific gravity: 5.9 to 6.4
Hardness: 5 to 5½
Streak: light yellowish, brownish
Colour: pale yellow to reddish brown, sometimes emerald green
Solubility: Insoluble in water, hydrochloric and nitric acid; soluble with decomposition in sulphuric acid
Environments:

Plutonic igneous environments
Pegmatites

Microlite is found in granitic pegmatites, especially those rich in lepidolite or other lithium-bearing minerals, and in albite

Millerite

Formula: NiS sulphide
Specific gravity: 5.3
Hardness: 3½
Streak: Dark green
Colour: Brass-yellow
Solubility: Insoluble in hydrochloric acid and sulphuric acid; moderately soluble in nitric acid
Environments:

Hydrothermal environments

Millerite forms as a low-temperature mineral often in cavities and as an alteration of other nickel minerals, or as crystal inclusions in other minerals. Millerite occurs in nickel deposits, as an alteration product of other nickel ores.

Common impurities: Fe,Co,Cu

Millisite

Formula: NaCaAl6(PO4)4(OH)9.3H2O hydrated phosphate containing hydroxyl, wardite group
Specific gravity: 2.83
Hardness: 5½
Streak: White
Colour: White to light grey, colourless in transmitted light.
Environments:

Hydrothermal environments

Millisite is found in altered phosphate deposits. At the type locality, the Little Green Monster Mine, Utah, USA, it is associated with dehrnite, lewistonite and wardite.

Mimetite

Formula: Pb5(AsO4)3Cl arsenate
Specific gravity: 7.1
Hardness: 3½ to 4
Streak: White
Colour: Colourless, white, brown, orange, yellow, green, grey
Solubility: Slightly soluble in hydrochloric acid and sulphuric acid; moderately soluble in nitric acid
Environments:

Hydrothermal environments

Mimetite is a secondary mineral occurring in the oxidation zone of high temperature hydrothermal lead deposits that also bear arsenic-containing minerals. While pyromorphite usually occurs only in the uppermost zones, mimetite can also appear in deeper deposit regions

Alteration

Solubility of mimetite
Pb5(AsO4)3Cl (solid) + 6H+ (aqueous) ⇌ 5Pb2+ (aqueous) + 3H2AsO-4 (aqueous) + Cl- (aqueous)

cerussite and aqueous H2AsO4-, Cl- and H+ to mimetite and aqueous H2CO3
5PbCO3 + 3H2AsO4- + Cl- + 7H+ ⇌ Pb5(AsO4)3Cl + 5H2CO3
or
5PbCO3 + 3HAsO42- + Cl- + 4H+ ⇌ Pb5(AsO4)3Cl + 5H2CO3
cerussite and mimetite can co-exist only under basic conditions at rather high PCO2.

Common impurities: Ca,F,Cr,V

Minium

Formula: Pb2+2Pb4+O4 multiple oxide
Specific gravity: 9.05
Hardness: 2½
Streak: Orange-yellow
Colour: Red to brownish red
Solubility: Soluble in hydrochloric acid with evolution of Cl2. Decomposed by nitric acid, with brown residue of PbO2
Environments:

Metamorphic environments

Minium occurs in the oxidised portions of lead ore deposits. It is associated with native lead and galena at the Jay Gould Mine, Idaho, USA, with galena, cerussite and iron oxides at Leadville, Colorado, USA, with massicot and cerussite at the Santa Fe mine, Mexico, and with native lead at Långban, Sweden.

Mirabilite

Formula: Na2(SO4).10H2O
Specific gravity: 1.490
Hardness: 1½ to 2
Streak: White
Colour: Colourless, white
Solubility: Soluble in water
Environments:

Sedimentary environments

Mirabilite occurs in salt lakes, playas and springs, and as an efflorescence on alkali soils. At Great Salt Lake, Utah, USA, it crystallises during winter due to decreased solubility at low temperatures.

Alteration: Mirabilite is unstable in dry air, when it loses its water and alters to thénardite, either as pseudomorphs after mirabilite, or just crumbled to a loose powder.

Mixite

Formula: Cu6Bi(AsO4)3(OH)6.3H2O
Hydrated arsenate with hydroxyl, mixite group
Specific gravity: 3.79
Hardness: 3 to 4
Streak: Lighter than colour
Colour: Emerald green to blue-green to whitish
Environments:

Hydrothermal environments

Mixite is an uncommon secondary mineral in the oxidised zone of bismuth-bearing copper deposits, associated with bismutite, skutterudite, bismuth, atelestite, erythrite, malachite and baryte.

At the type locality, Jáchymov, Bohemia, Czech Republic, mixite occurs with bismutite, smaltite, skutterudite and native bismuth.

At the St Anton mine and Humbachtal, Wittichen District, Germany, mixite occurs with erythrite and baryte.

At the San Rafael mine, Nye county, Nevada, USA, mixite is associated with plumbojarosite, olivenite and kaolinite.

Molybdenite

Formula: MoS2 sulphide
Specific gravity: 4.7 to 4.8
Hardness: 1 - 1½
Streak: Dark grey
Colour: Lead-grey
Solubility: Moderately soluble in sulphuric and nitric acid
Environments:

Plutonic igneous environments
Pegmatites
Metamorphic environments
Hydrothermal environments

Molybdenite forms as an accessory mineral in some igneous rocks and in pegmatites. It is found in contact metamorphic deposits, and it is important in disseminated deposits of the porphyry (with coarse crystals or mineral grains phenocrysts in a finer groundmass) type. It is common as a primary mineral in hypothermal (high temperature) hydrothermal veins.
Molybdenite may be found in some granites, including aplite
In contact metamorphic deposits it is associated with lime silicates, scheelite and chalcopyrite.
In hypothermal (high temperature) hydrothermal veins it is associated with cassiterite, scheelite, hübnerite-ferberite and fluorite.

Monazite-(Ce)

Monazite-(Ce) is the overwhelmingly most common member of the monazite group. Formula: Ce(PO4) phosphate
Specific gravity: 5 to 5.5
Hardness: 5 to 5½
Streak: White
Colour: Commonly reddish brown to brown; shades of green to brown, yellow brown, rarely nearly white; yellow, colourless in transmitted light.
Solubility: Slightly soluble in hydrochloric, sulphuric and nitric acid
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites
Sedimentary environments
Metamorphic environments
Hydrothermal environments (infrequent)

Monazite is a comparatively rare mineral occurring as an accessory in some plutonic igneous rocks, in pegmatites and as rolled grains in sands because of its resistance to chemical attack and its high specific gravity.
It may be found in granite including aplite, syenite, schist, gneiss and granulite.
In clastic sedimentary deposits it is associated with other resistant and heavy minerals such as magnetite, ilmenite, rutile and zircon.
At Llallagua, Bolvia, monazite occurs both as an igneous mineral, with a high thorium content, and also as a hydrothemal mineral, with a characteristically low thorium content. It is associated with fluorapatite, other hydrous phosphates and cassiterite. As the temperature drops, monazite begins to crystallise out at about 550oC and continues on down to about 300oC, when most of the cassiterite crystallises.

Montgomeryite

Formula: Ca4MgAl4(PO4)6(OH)4.12H2O hydrated phosphate with hydroxyl, montgomeryite group
Specific gravity: 2.530
Hardness: 4
Streak: White
Colour: Dark green to light green, colourless, red, yellow
Environments:

Pegmatites
Hydrothermal environments

Montgomeryite is a secondary mineral in sedimentary phosphate nodules and a late-stage mineral in highly oxidized phosphate nodules in granitic pegmatites. At the Little Green Monster Mine, Utah, USA, it occurs associated with wardite, englishite, gordonite, crandallite and apatite.

Monticellite

Formula: CaMg(SiO4) nesosilicate (insular SiO4 groups) olivine group
Specific gravity: 3.2
Hardness: 5½
Streak: White
Colour: Colourless, grey or greenish
Solubility: Insoluble in water, nitric and sulphuric acid; soluble with gelatinous residue in hydrochloric acid
Environments:

Volcanic igneous environments
Carbonatites
Metamorphic environments

Monticellite occurs as a relatively common mineral formed during metamorphism of siliceous olivine dolostones, in contact metamorphic deposits between limestones and olivine gabbros and in skarns at granite-dolomitic limestone contacts. It occurs less frequently in kimberlites.
It is a mineral of the granulite facies.

Alteration

During the progressive metamorphism of silica-rich dolostones the following approximate sequence of mineral formation is often found, beginning with the lowest temperature product: talc, tremolite, diopside, forsterite, wollastonite, periclase, monticellite

åkermanite to monticellite and wollastonite
Ca2MgSi2O7 → CaMg(SiO4) + CaSiO3

diopside, forsterite and calcite to monticellite and CO2
CaMgSi2O6 + Mg2SiO4 + 2CaCO3 → 3CaMgSiO4 + 2CO2
This reaction requires a high temperature.

forsterite and åkermanite to diopside and monticellite
Mg2SiO4 + 2Ca2MgSi2O7 → CaMgSi2O6 + 3CaMg(SiO4)

forsterite, calcite and quartz to monticellite and CO2
Mg2SiO4 + 2 CaCO3 + SiO2 → 2CaMg(SiO4) + 2 CO2

forsterite, diopside and calcite to monticellite and CO2
Mg2SiO4 + CaMgSi2O6 + 2 CaCO3 ⇌ 3CaMg(SiO4) + 2 CO2
This reaction occurs during contact metamorphism of magnesian limestone.

grossular, diopside, monticellite, calcite and H2O to vesuvianite, quartz and CO2
10Ca3Al2(SiO4)3 + 3CaMgSi2O6 + 3CaMg(SiO4) + 2CaCO3 + 8H2O ⇌ 2Ca19Al10Mg3(SiO4)10 (Si2O2)4O2(OH)8 + 3SiO2 + 2CO2
A common association in calc-silicate metamorphism can be represented by the above equation. Vesuvianite stability will tend to increase with increasing water and decrease as the activity of CO2 rises.

monticellite and CO2 to åkermanite, forsterite and calcite
3CaMgSiO4 + CO2 ⇌ Ca2MgSi27 + Mg2O7 + CaCO3
At 4.3 kbar pressure the equilibrium temperature is about 890oC (granulite facies).

monticellite and diopside to åkermanite and forsterite
3CaMgSiO4 + CaMgSi2O6 ⇌ 2Ca2MgSi2O7 + Mg2O7
At a pressure of 4.3 kbar the equilibrium temperature is about 890oC (granulite facies).

monticellite and spurrite to merwinite and calcite
2CaMg(SiO4) + Ca5(SiO4)2(CO3) ⇌ 2Ca3Mg(SiO4)2 + CaCO3

monticellite, spurrite and quartz to merwinite and CO2
5CaMg(SiO4) + Ca5(SiO4)2(CO3) + SiO2 ⇌ 5Ca3Mg(SiO4)2 + 2CO2

Common impurities: Ti,Al,Fe,Mn,Zn,H2O

Montmorillonite

Formula: (Na,Ca)0.3(Al,Mg)2Si4O10(OH)2(OH)2. nH2O phyllosilicate (sheet silicate)
Specific gravity: 2.0 to 2.7
Hardness: 1 to 2
Streak: White
Colour: White, buff, yellow, green, rarely pale pink to red. Pink to red coloration is due to high valance Mn
Environments:

Sedimentary environments

Montmorillonite is a common clay mineral. It is an alteration product of volcanic tuff and ash, or it may precipitate from water. It forms under alkaline conditions of poor drainage, and is stable up to about 140oC. It is a zeolite facies mineral.

Alteration

albite and montmorillonite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz and H2O
8Na(AlSi3O8) + 2Ca0.5(Mg3.5Al0.5)Si8O20(OH)4.nH2O → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 15SiO2 + 6H2O
This reaction occurs in low to intermediate metatmorphism.

montmorillonite and K-feldspar to illite, aqueous SiO2 and H2O
Al2Si4O10(OH)2.nH2 + KAlSi3O8 → KAl2(AlSi3)O10(OH)2 + 4SiO2 + nH2O

Common impurities: Fe,K

Mordenite

Formula: (Na2,Ca,K2)4(Al8Si40)O96.28H2O tectosilicate (framework silicate), zeolite group
Specific gravity: 2.10 to 2.15
Hardness: 4 to 5
Streak: White
Colour: Colourless, white, yellow, pink, orange, red
Environments:

Volcanic Igneous environments
Sedimentary environments
Hydrothermal environments
Basaltic cavities

Mordenite occurs in silica rich (eg rhyolitic) volcanics, in volcanic ash beds, tuff, and rarely in olivine-basalt. It is of hydrothermal or sedimentary authigenic (formed in place) origin.
Common impurities: Mg

Mottramite

Formula: PbCu(VO4)(OH) anhydrous vanadate containing hydroxyl
Duhamelite is a variety of mottramite
Specific gravity: 5.9
Hardness: 3 to 3½
Streak: Yellowish
Colour: Grass-green, olive-green, yellow-green, siskin-green, blackish brown, nearly black
Solubility: Readily soluble in acids
Environments:

Hydrothermal environments

Mottramite is a secondary mineral associated with descloizite in oxidised zones, especially in sandstone.
Common impurities: Zn

Muscovite

Formula: KAl2(AlSi3O10)(OH)2 phyllosilicate (sheet silicate), mica group
Muscovite forms a continuous series with celadonite KMgFe3+Si4O10(OH)2

Illite series minerals are K-deficient varieties of muscovite
Sericite is a variety of muscovite
Specific gravity: 2.77 to 2.88
Hardness: 2½
Streak: White
Colour: White, yellow
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments (muscovite):

Plutonic igneous environments
Pegmatites
Sedimentary environments
Metamorphic environments
Hydrothermal environments

In the Bowen reaction series muscovite is intermediate between orthoclase (higher temperature) and quartz (lower temperature).
Muscovite is a widespread and common rock-forming mineral. It is a primary mineral typically found in granite and granite pegmatites, where it is associated with quartz and feldspar.
Muscovite occurs in detrital and authigenic (formed in place) sediments.
Muscovite is also very common in metamorphic rocks, being the chief constituent of some mica schists. It occurs in every zone of progressive regional metamorphism. In the chlorite zone muscovite is a characteristic constituent of albite-chlorite-sericite (variety of muscovite) schist. In the biotite zone muscovite is less common than in the chlorite zone, because muscovite reacts with chlorite to form phlogopite and amesite.
Muscovite is a mineral of the albite-epidote-hornfels, hornblende-hornfels, prehnite-pumpellyite, greenschist, amphibolite, blueschist and eclogite facies.

Muscovite is an essential constituent of phyllite, and a common constituent of granite. It also may be found in gneiss, schist and amphibolite

At Yaogangxian, Hunan, China, muscovite sometimes occurs coating earlier formed arsenopyrite and ferberite.

At the Santo Nino mine, Arizona, USA, muscovite encloses rutile.

At the Chickering mine, New Hampshire, USA, muscovite is a component of the outer pegmatite zones, having formed before the melt became enriched in lithium in the inner zones, forming the lithium-rich mica lepidolite. It also occurs much later as a druse lining moulds where elbaite crystals have dissolved.

The illite series minerals are varieties of muscovite that frequently contain montmorillonite/beidellite layers. They occur as constituents of some shale, soil and recent sediments. Illite is a mineral of the zeolite and prehnite-pumpellyite facies. In the zeolite facies clay minerals transform to illite, kaolinite and vermiculite.

Sericite is a variety of muscovite that occurs as fibrous aggregates with a silky lustre.
Environments (sericite):

Pegmatites
Metamorphic environments

The development of sericite from feldspar and other minerals, such as topaz, kyanite, spodumene, and andalusite, is a common feature of retrograde metamorphism. Sericite also forms as an alteration of the wall rock of hydrothermal ore veins.

Alteration

The fine-grained "pinite", which is mainly composed of muscovite and clay minerals, occurs as an alteration product of cordierite.

antigorite and muscovite to phlogopite, amesite, SiO2 and H2O
5Mg3Si2O5(OH)4 + 3KAl2(AlSi3O10)(OH)2 → 3KMg3(AlSi3O10)(OH)2 + 3Mg2Al(AlSiO5)(OH)4 + 7SiO2 + 4H2O

chlorite, muscovite and quartz to biotite, Fe-rich cordierite and H2O
(Mg,Fe2+)5Al(AlSi3O10)(OH)8 + KAl2(AlSi3O10)(OH)2 + 2SiO2 → K(Mg,Fe2+)3(AlSi3O10)(OH)2 + (Mg,Fe2+)2Al4Si5O18 + 4H2O
This reaction ocurs when the metamorphic grade increases

K-feldspar and H+ to muscovite, silica and K+
3KaAlSi3O8 + 2H+ ⇌ KAl2(AlSi3O100(OH)2 + 6SiO2 (aqueous) + 2K+
Low temperature and a low K+/H+ ratio favour the forward reaction.

montmorillonite and K-feldspar to illite (variety of muscovite), aqueous SiO2 and H2O
Al2Si4O10(OH)2.nH2 + KAlSi3O8 ⇌ KAl2(AlSi3)O10(OH)2 + 4SiO2 + nH2O

muscovite to corundum, K-feldspar and H2O
KAl2(AlSi3O10)(OH)2 ⇌ Al2O3 + K(AlSi3O8) + H2O
This reaction takes place above temperatures ranging from 600oC at atmospheric pressure (hornblende-hornfels facies) to about 720oC at pressure above 4 kbar (amphibolite facies).

muscovite, H+ and H2O to kaolinite and K+
2KAl2(AlSi3O10)(OH)2 + 2H+ + 3H2O ⇌ 3Al2Si2O5(OH)4 + 2K+
Low temperature and a low K+/H+ ratio favour the forward reaction.

muscovite, biotite and SiO2 to K-feldspar, garnet and H2O
KAl2(AlSi3O10)(OH)2 + K(Fe2+,Mg)3(AlSi3O10)(OH)2 + 3SiO2 → 2KAlSi3O8 + (Fe2+,Mg)3Al2(SiO4)3 + 2H2O

muscovite and garnet to biotite, sillimanite and quartz
KAl2(AlSi3O10)(OH)2 + (Fe2+,Mg)3Al2(SiO4)3 → K(Fe2+,Mg)3(AlSi3O10)(OH)2 + 2Al2SiO5 + SiO2
Muscovite is unstable in combination with garnet.

muscovite and quartz to sillimanite, K-feldspar and H2O
KAl2(AlSi3O10)(OH)2 + SiO2 ⇌ Al2SiO5 + KAlSi3O8 + H2O
At 5 kbar pressure the equilibrium temperature is about 690oC (amphibolite facies)
The forward reaction is strongly endothermic (absorbs heat) and the reverse reaction in exothermic (gives out heat), hence the forward reaction is favoured by high temperatures, as the system adjusts to bring the temperature back down.
Although the muscovite-quartz assemblage is stable over a large part of the PT range of regional metamorphism, at temperatures around 600 to 650oC it is replaced by sillimanite and K-feldspar.

sillimanite, annite and H2O to staurolite, muscovite, SiO2 and O2
31Al2SiO5 + 4KFe2+3(AlSi3O10)(OH)2 + 6H2O → 34Fe2+2Al9si4O23(OH) + KAl2 (AlSi3O10)(OH)2 + 7 SiO2 + 1.5O2
Staurolite may occur as a product of retrograde metamorphism according to the above reaction.

spodumene, K+ and H+ to muscovite, quartz and Li+
3LiAlSi2O6 + K+ + 2H+ → KAl3Si3O10(OH)2 + 3SiO2 + 3Li+
The direct conversion of spodumene to muscovite liberates silica, but quartz is not usually present in pseudomorphs of muscovite after spodumene, and this requires an explanation.

staurolite, annite and O2 to hercynite, magnetite, muscovite,corundum, SiO2 and H2O
2Fe2+2Al9Si4O23(OH) + KFe2+3 (AlSi3O10)(OH)2 +2O2 → 4Fe2+Al2O4 + Fe2+Fe3+2O4 + KAl2 (AlSi3O10)OH)2 + 4Al2O3 + 8SiO2 + 2H2O

Other reactions:
The fine-grained variety sericite replaces beryl, topaz and tourmaline in pegmatites.
Muscovite itself alters to illite.

Common impurities: Cr,Li,Fe,V,Mn,Na,Cs,Rb,Ca,Mg,H2O

Nahcolite

Formula: NaH(CO3) acid carbonate
Specific gravity: 2.21
Hardness: 2½
Streak: White
Colour: Colourless, white, grey, buff
Solubility: Readily soluble in water forming an alkaline solution that gives off carbon dioxide when heated. Also soluble in glycerine.
Environments

Sedimentary environments

Nahcolite is a lacustrine (lake) evaporite mineral.

Localities

Italy

In old Roman conduit at Naples, Italy, nahcolite occurs admixed with trona and thermonatrite as an efflorescence.

Kenya

In Little Lake Mogadi, Kenya, it occurs as fibrous pseudomorphs after gaylussite, and as alteration rims around thermonatrite.

USA

At Searles Lake, California, nahcolite occurs in thin beds associated with gaylussite, thénardite, burkeite, northupite, borax and halite.

Namibite

Formula: Cu(BiO)2(VO4)(OH)
Specific gravity: 6.86
Hardness: 4½ to 5
Streak: Pistachio green
Colour: Dark green
Solubility: Easily soluble in cold dilute acids
Environments:

Pegmatites
Hydrothermal environments

Namibite is a secondary mineral in bismuth-bearing hydrothermal polymetallic mineral deposits and granite pegmatites, associated with bismuth, bismutite, wittichenite, bismite, bismutostibiconite, bismutoferrite, clinobisvanite, pucherite, beyerite, schumacherite, mixite, eulytite and chrysocolla.

At the type locality, a copper mine near Khorixas, northwestern Namibia, namibite occurs in cavities in drusy quartz veins associated with beyerite, native bismuth, bismite, bismutite and oxidised copper minerals.

Natrite

Formula: Na2CO3 anhydrous carbonate
Specific gravity: 2.54
Hardness: 3½
Streak: White
Colour: Grey-white to colourless
Solubility: Soluble in water
Environments:

Sedimentary environments

Natrite occurs in deep workings and drill cores in mines in evaporite rocks in the Kola Peninsula, Russia. In air it rapidly hydrates to thermonatrite.

Natrolite

Formula: Na2(Si3Al2)O10.2H2O tectosilicate (framework silicate), zeolite group
Specific gravity: 2.2 to 2.4
Hardness: 5 to 5½
Streak: White
Colour: Colourless, white, yellow
Solubility: Moderately soluble in hydrochloric acid
Environments:

Plutonic igneous environments
Pegmatites
Basaltic cavities

Natrolite is characteristically found lining cavities in basalt associated with other zeolites and calcite; it is one of the later zeolites to crystallise. It is also found in syenite and nepheline syenite.
Geothermal wells have been drilled through a thick series of basalt flows in western Iceland, where it was found that natrolite crystallised at temperatures from 70oC to 100oC at depths between 450m and 1200m.
It may also be an alteration product of nepheline, sodalite or plagioclase.

At Kragerø, Telemark, Norway, natrolite occurs on joint surfaces in a quartz-rich gneiss, associated with stilbite, heulandite and laumontite.

In the basalts of northern Ireland, UK, natrolite typically occurs in cavities associated with analcime, often together with chabazite and calcite.

Common impurities: Ca,K

Natron

Formula: Na2CO3.10H2O hydrated normal carbonate
Specific gravity: 1.478
Hardness: 1
Streak: White
Colour: Colourless, white, grey, yellow
Solubility: Soluble in water forming alkali solution, effervesces in acid.
Environments:

Sedimentary environments

On slight heating natron decomposes thermonatrite and H2O. It forms from water solution below 32oC but when other salts are present the temperature limit may be lower. It occurs in soda lakes. In the Eastern Gobi desert it is associated with thermonatrite, trona, gaylussite and calcite.

Neotocite

Formula: (Mn,Fe)SiO3.H2O(?) phyllosilicate (sheet silicate)
Forms a series with hisingerite
Specific gravity: 2.43
Hardness: 3 to 4
Streak: Brown
Colour: Black, dark brown to dark olive-green, dark red-brown
Solubility: Decomposed by hydrochloric acid
Environments:

Pegmatites
Hydrothermal environments

Neotocite is a secondary mineral formed from the alteration of rhodonite and other manganese silicates, associated with rhodonite, calcite and quartz. It is frequently found as veins in weathered manganese-bearing pyroxenes, especially rhodonite, and also in spessartine. It is also found lining fractures in granite pegmatites.

Common impurities: Al,Mg,Ca,Na,K,C

Nepheline

Formula: NaAlSiO4 tectosilicate (framework silicate), feldspathoid
Nepheline forms partial solid solutions with both albite and anorthite.
Specific gravity: 2.6 to 2.7
Hardness: 5 - 6
Streak: White
Colour: Colourless, white, grey, yellow to brownish, reddish and greenish
Solubility: Readily soluble in hydrochloric acid
Environments:

Plutonic igneous rocks
Volcanic igneous environments
Pegmatites
Carbonatites

Nepheline is a primary rock-forming mineral that requires a high soda and low silica environment, and it never occurs together with quartz. It is the characteristic mineral of the alkaline rocks and it is the most common of the feldspathoid minerals. It is associated with alkali feldspars in nepheline syenite and nepheline gneiss, and with plagioclase in alkaline gabbro.
In alkaline rocks nepheline is associated with olivine, augite, diopside and sodium-rich pyroxenes and amphiboles, but not with orthopyroxene or pigeonite.
In some calcium-rich basic rocks nepheline occurs with melilite, monticellite and wollastonite.
In some potassium-rich hypabyssal rocks (intrusive igneous rocks that originate at medium to shallow depths within the crust) and volcanic rocks, nepheline occurs with leucite.

Nepheline may be found in andesite, basalt, diorite, gabbro, mafic igneous rocks (characteristic), syenite and trachyte.

For pure nepheline, the low temperature phase is stable up to about 900oC, when it inverts to the high temperature phase, which is stable up to 1254oC.

Alteration

Nepheline frequently alters to analcime, cancrinite, sodalite, natrolite and thomsonite.
In the nepheline gneiss of southeastern Ontario, Canada, nepheline is altered by low temperature hydrothermal activity to natrolite, muscovite, hydronepheline and gieseckite.

albite to nepheline and quartz
Na(AlSi3O8) ⇌ NaAlSiO4 + 2SiO2

jadeite to nepheline and albite
2NaAlSi2O6 ⇌ NaAlSiO4 + NaAlSi3O8
At 20 kbar pressure the equilibrium temperature is about 1,000oC (eclogite facies), with equilibrium to the right at higher temperatures and to the left at lower temperatures.

nepheline and NaCl from the fluid to sodalite
6NaAlSiO4 + NaCl ⇌ 2Na4(Si3Al3)O12Cl
At the Igaliko Complex, South Greenland, sodalite is formed by replacement of nepheline, leading to a volume change which in turn causes a network of fractures. Deep blue fluorescent fluorite forms in these fractures, because the reaction of nepheline changing to sodalite reduces the salinity of the fluid, hence reducing the solubility of fluorite, so it precipitates.

nepheline and H4SiO4 (silicic acid) to analcime and H2O
NaAlSiO4 + H4SiO4 ⇌ Na(AlSi2O6).H2O + H2O

nepheline and diopside to melilite, forsterite and albite
3NaAlSiO4 + 8CaMgSi2O6 ⇌ 4Ca2MgSi2O7 + 2Mg2SiO4 + 3NaAlSi3O8
This reaction is in equilibrium at about 1180oC, with lower temperatures favouring the forward reaction.

Common impurities: Mg,Ca,H2O

Nontronite

Formula: Na0.3Fe3+2(Si,Al)4O10(OH)2.nH2O phyllosilicate
Specific Gravity: 2.06 to 2.32
Hardness: 1 to 2
Streak: White
Colour: Green, olive-green, yellow-green, yellow, orange, brown
Environments:

Volcanic igneous environments
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Nontronite is a weathering product of basalt and other mafic and ultra-mafic volcanic rocks. It also occurs in poorly drained volcanic ash soils, in some hydrothermally altered mineral deposits, and contact metamorphosed limestone. It is authigenic (formed in place) in recent marine sediments. It is formed in the presence of both neutral and acid cool hydrothermal fluids, and is stable up to about 140oC.

Common impurities: Ti,Mg,Ca

Northupite

Formula: Na3Mg(CO3)2Cl anhydrous carbonate containing halogen
Specific gravity: 2.38
Hardness: 3½
Streak: White
Colour: Colourless, pale yellow, grey, brown
Solubility: Readily soluble in dilute acids with effervescence. Decomposed by hot water with the separation of magnesium carbonate.
Environments:

Sedimentary environments
Sedimentary environments

Northupite occurs in continental evaporite deposits and in oil shales. At Searles Lake, California, USA it is associated with tychite, pirssonite and rarely burkeite and nahcolite, and at Borax Lake with gaylussite and pirssonite. In drill cores in the oil shales at Green River, Wyoming, USA, it occurs with shortite, bradleyite, trona, pirssonite and gaylussite.

Offretite

Formula: KCaMg(Si13Al5)O36.15H2O tectosilicate (framework silicate) zeolite group
Specific gravity: 2.10 to 2.13
Hardness: 4
Streak: White
Colour: Colourless, white, yellow, golden
Environments:

Volcanic igneous environments
Hydrothermal environments

Offretite occurs in veins and fractures in basaltic rocks, usually intergrown with erionite or as epitaxial overgrowths on it. Offretite is not found in Si-rich volcanics, pegmatites or altered volcanic ash tuff (where erionite is abundant). Offretite is of hydrothermal origin. At Passo Forcal Rosso, Italy, chabazite-offretite epitaxial overgrowths occur. In Hunter Valley, NSW, Australia offretite occurs on plates of lévyne.
Common impurities: Mg

Okenite

Formula: Ca10Si18O46.18H2O phyllosilicate
Specific Gravity: 2.28 to 2.33
Hardness: 4½ to 5
Streak: White
Colour: Colourless, white, pale yellow, blue
Environments:

Carbonatites
Basaltic cavities

Okenite occurs in cavities in basalt or related eruptive rocks. In limestone at Crestmore, California, USA, and in carbonatites. It is often associated with zeolites, apophyllite, calcite, prehnite and quartz.
Common impurities: Al,Fe,Sr,Na,K

Olivenite

Formula: Cu2(AsO4)(OH)
Anhydrous arsenate containing hydroxyl. Olivenite group, forms series with libethenite and with adamite.
Specific gravity: 3.9 to 4.5
Hardness: 3
Streak: Olive-green to brown
Colour: Olive green to yellow or brown, grey-green, greyish white; light green in transmitted light.
Solubility: Soluble in acids and in ammonia
Environments:

Hydrothermal environments

Olivenite is a relatively common, thermodynamically very stable, secondary copper mineral found in the oxidised zones of copper deposits containing arsenic-bearing phases, especially tennantite and enargite. It is the most common secondary copper arsenate in the oxdised zone of hydrothermal copper deposits.

Associations: clinoclase, conichalcite, tyrolite, cornetite, cornwallite, metazeunerite, scorodite, pharmacosiderite, spangolite, chalcophyllite, brochantite, malachite, azurite and chrysocolla.

At the Block 14 open cut, Broken Hill, New South Wales, Australia, olivenite occurs with beudantite-segnitite, bayldonite, mawbyite and mimetite. Later sulphate minerals such as brochantite and linarite also occur on some specimens.

At the New Cobar deposit, New South Wales, Australia, olivenite occurs in vugs in quartz, associated with chenevixite and agardite, and almost always associated with partially oxidised arsenopyrite.

At the Desolation prospect, Mount Isa Block, Queensland, Australia, olivenite is found on chrysocolla, associated with clinoclase. Olivenite and libethenite also occur on earlier chrysocolla and As-rich pseudomalachite crusts.

At the Bali Lo prospect, Ashburton Downs, Western Australia, olivenite occurs intergrown with chenevixite.

At the Telfer gold mine, Western Australia, olivenite has been found radiating from cavity surfaces in quartz veins overgrown by chrysocolla.

At the Clara mine, Near Wolfach in the Black Forest, Germany, olivenite and its associated minerals agardite-(Ce), cornwallite and clinoclase, are perched on a fluorite and/or baryte matrix with disseminated tetrahedrite-tennantite. Also an olivenite-adamite solid solution is found associated with phillipsburgite.

At Ightem, Bou Azzer, Morocco, zinc-rich olivenite occurs associated with powellite.

At Tamdrost-West, Bou Azzer, Morocco, cobalt- and nickel-rich olivenite has been found in cavities in quartz associated with pharmacosiderite.

At the San Rafael mine, Nye county, Nevada, USA, olivenite occurs within zones containing mixite and conichalcite in the rosasite stope. Olivenite has also been documented here in association with cornubite and cornwallite.

At the Majuba mine, Pershing county, Nevada, USA, olivenite is associated with cornetite.

At the Mammoth mines, Tintic district, Utah, USA, olivenite is associated with clinoclase, tyrolite and conichalcite.

Common impurities: Fe,P

Olivine

Olivine is a series between forsterite Mg2SiO4 and fayalite Fe2SiO4. These are both nesosilicates (insular SiO4 groups).
Solubility: Insoluble in water, nitric and sulphuric acid; soluble in hydrochloric acid
Environments:

Plutonic igneous environments
Volcanic igneous environments

Olivine is a common primary, rock-forming mineral, varying in amount from an accessory to a major constituent. It is the first major mineral to crystallise in the discontinuous branch of the Bowen reaction series.
Olivine is an essentail constituent of kimberlite. It is a common constituent of gabbro, dunite, peridotite and basalt.
It also may be found in andesite, diorite, gabbro, granite,
It is associated with plagioclase feldspar, pyroxene, magnetite, corundum, chromite and serpentine.
quartz never occurs with olivine.
Olivine is a mineral of the granulite facies.

Alteration

cummingtonite-grunerite and olivine to enstatite-ferrosilite and H2O
(Fe,Mg)7Si8O22(OH)2 + (Mg,Fe)2SiO4 ⇌ 9(Mg,Fe2+)SiO3 + H2O

enstatite-ferrosilite, Fe-rich diopside and Fe, Cr-rich spinel to garnet and olivine
2(Mg,Fe2+)SiO3 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4

Mg-rich greenalite to olivine, Mg-rich grunerite and H2O
18(Fe2+, Mg))3Si2O5(OH)4 → 20(Fe,Mg)2SiO4 + 2(Fe2+,Mg)7Si8O22(OH)2 + 34H2O

Mg-rich greenalite to olivine, SiO2 and H2O
2(Fe2+, Mg))3Si2O5(OH)4 → 3(Fe,Mg)2SiO4 + SiO2 + 4H2O

hypersthene, augite and Fe and Cr-rich spinel to garnet and olivine
2(Mg,Fe)SiO3 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4

olivine and CO2 to enstatite- ferrosilite and magnesite-siderite
(Mg,Fe)2SiO4 + CO2 → (Mg,Fe2+)SiO3 + (Mg,Fe)CO3

olivine and H2O to serpentine, magnetite and H2
6(Mg1.5Fe0.5)SiO4 + 7H2O → 3Mg3Si2O5(OH)4 + Fe2+Fe3+2O4 + H2
The iron Fe in olivine does not enter into the serpentine, but recrystallises as magnetite.

olivine and quartz to enstatite-ferrosilite
(Mg,Fe)2SiO4 + SiO2 → 2(Mg,Fe2+)SiO3

orthopyroxene, Fe-rich diopside and Fe and Cr-rich spinel to Fe, Ca and Cr-rich pyrope and olivine
(Mg,Fe)2Si2O6 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ (Mg,Fe)2Ca(Al,Cr)2Si3O12 + (Mg,Fe)2Ca(Al,Cr)2Si3O12 + (Fe,Mg)2SiO4
The garnet-bearing peridotites are considered to have originated in a high-pressure environment according to the reaction

Mg-rich siderite and quartz to olivine, orthopyroxene and CO2
3(Fe,Mg)(CO3)→ (Fe,Mg)2SiO4 + 2SiO2 → (Fe,Mg)2SiO4 + 3CO2

Omphacite

Formula: (Ca,Na)(Mg,Fe,Al)Si2O6 inosilicate (chain silicate) pyroxene group
Specific gravity: 3.29 to 3.39
Hardness: 5 - 6
Streak: Greenish white
Colour: Dark green
Environments:

Metamorphic environments

Omphacite is an essential constituent of eclogite as a result of high pressure and high temperature metamorphism.
It is also found in kimberlites.
It is a characteristic mineral of the eclogite facies.

Alteration

amphibole, chlorite, paragonite, ilmenite, quartz and calcite to garnet, omphacite, rutile, H2O and CO2
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + Mg5Al(AlSi3O10)(OH)8 + 3NaAl2(Si3Al)O10(OH)2 + 4Fe2+Ti4+O3 + 9SiO2 + 4CaCO3 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 8H2O + 4CO2
In low-grade rocks relatively rich in calcite the garnet-omphacite association may be due to reactions such as the above.

amphibole, clinozoisite, chlorite, albite, ilmenite and quartz to garnet, omphacite, rutile and H2O
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + 2Ca2Al3[Si2o7][SiO4]O(OH) + Mg5Al(AlSi3O10)(OH)8 + 3NaAlSi3O8 + 4Fe2+Ti4+O3 + 3SiO2 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 6H2O

In low-grade rocks relatively poor in calcite the garnet-omphacite association may be developed by the above reaction.

augite, albite, pyroxene, anorthite and ilmenite to omphacite, garnet, quartz and rutile
2MgFe2+Si2O6 + Na(AlSi3O8) + Ca2Mg2Fe2+Fe3+AlSi5O18 + 2Ca(Al2Si2O8) + 2Fe2+Ti4+O3 → NaCa2MgFe2+Al(Si2O6)3 + (Ca2Mg3Fe2+4)(Fe3+Al5)(SiO4)9 + SiO2 + 2TiO2
This reaction occurs at high temperature and pressure.

diopside and albite to omphacite and quartz
CaMgSi2O6 + xNaAlSi3O8 ⇌ CaMgSi2O6.xNaAlSi2O6 + SiO2

labradorite, albite, forsterite and diopside to omphacite, garnet and quartz
3CaAl2Si2O8 + 2Na(AlSi3O8) + 3Mg2SiO4 + nCaMgSi2O6 → (2NaAlSi2O6 + nCaMgSi2O6) + 3(CaMg2)Al2(SiO4)3 + 2SiO2

Common impurities:Ti,Cr,Mn,K,H2O

Opal

Formula: SiO2.nH2O tectosilicate (framework silicate)
Specific gravity: 1.9 -2.2
Hardness: 5 - 6½
Streak: White
Colour: Colourless, transparent (variety hyalite), whitish, bluish with a play of rainbow colours (precious opal), red to orange, translucent (fire opal), green, red, brown, yellow, opaque (common opal)
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Volcanic igneous environments
Pegmatites
Sedimentary environments
Basaltic cavities
Hot spring deposits

Opal is a low temperature secondary mineral that develops in a wide variety of rocks as cavity and fracture fillings; it may be deposited by hot springs at shallow depths, and it may replace the cells in wood and the shells of clams. The largest accumulations of opal are formed from silica-secreting organisms.

Orientite

Formula: Ca8Mn3+10(SiO4)3(Si3O10)3(OH)10.4H2O
Sorosilicate (Si2O7 groups)
Specific gravity: 3.33
Hardness: 4½ to 5
Streak: Brown
Colour: Deep red to brown, maroon
Solubility: Soluble in hot hydrochloric acid; insoluble in nitric acid
Environments:

Sedimentary environments
Basaltic cavities

Orientite is of low temperature origin and forms in low alumina conditions, occurring with jasper, psilomelane, manganite and baryte.

At Lake Manganese, Keweenaw county, Michigan, USA, orientite is associated with manganite, braunite, macfallite and pyrolusite all replacing calcite in fissures and lenses in basalt.

At the type locality in what was Oriente Province, Cuba, orientite occurs in manganese ore bodies in trachyte-like rocks and andesite tuff, agglomerates and limestone, associated with todorokite, manganite, pyrolusite neotocite, ferruginous chalcedony, baryte, low quartz, calcite, analcime, stilbite, chabazite and laumontite.

Common impurities: Al,Fe,V,Cu,Mg,K,H2O,S

Orpiment

Formula: As2S3 sulphide
Specific gravity: 3.48
Hardness: 1½ to 2
Streak: Light yellow
Colour: Lemon yellow to orange yellow
Solubility: Slightly soluble in nitric acid
Environments:

Fumeroles and hot spring deposits
Hydrothermal environments

Orpiment is a rare mineral, usually associated with realgar and formed under similar conditions. It occurs in epithermal (low temperature) hydrothermal silver and lead ore veins, together with cinnabar, realgar and calcite. It is also found in hot springs and fumaroles. It is an alteration product of arsenic minerals, especially realgar.

Common impurities: Hg,Ge,Sb

Orthoclase

Formula: K(AlSi3O8) tectosilicate (framework silicate), K-feldspar.
Adularia is a more ordered low-temperature variety of orthoclase or partially disordered microcline.
Properties of orthoclase
Specific gravity: 2.55 to 2.63
Hardness: 6
Streak: White
Colour: White, green, yellow, pink
Solubility: Insoluble in hydrochloric acid, sulphuric and nitric acids
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites
Metamorphic environments
Hydrothermal environments

In the Bowen reaction series orthoclase is the first major mineral to crystallise after the two branches, continuous and discontinuous, combine.
Orthoclase is a mineral of the zeolite facies.
Adularia is a low temperature form of either orthoclase or partially disordered microcline. It occurs mainly in low temperature veins in gneiss and schist, where it is associated with low sulphidation, low temperature mineralisation. Increased pH (lower acidity) promotes stability of adularia over illite.

K-feldspars are essential constituents of granite and syenite, and major constituents of granodiorite. When these rocks have cooled at moderate depth and at reasonably fast rates orthoclase is the characteristic K-feldspar. In more slowly cooled granite and syenite microcline is the characteristic K-feldspar.

Alteration

biotite and quartz to enstatite-ferrosilite, orthoclase and H2O
K(Mg,Fe)3(AlSi3O10)(OH)2 + 3SiO2 → 3(Mg,Fe2+)SiO3 + KAlSi3O8 + H2O
Enstatite-ferrosilite may develop from the breakdown of biotite according to the above reaction.

Common impurities: Na,Fe,Ba,Rb,Ca

Overite

Formula: CaMgAl(PO4)2(OH).4H2O hydrated phosphate with hydroxyl, overite group
Specific gravity: 2.53
Hardness: 3½ to 4
Streak: White
Colour: Light apple-green to colourless; colourless in transmitted light
Solubility: Readily soluble in hot nitric acid
Environments:

Pegmatites
Hydrothermal environments

Overite is a secondary phosphate mineral found in altered phosphate nodules in sediments and in granitic pegmatites. At the type locality, Clay Canyon, Utah, USA, it is associated with crandallite and apatite.

Papagoite

Formula: CaCuAlSi2O6(OH)3
Cyclosilicate (ring silicate)
Specific gravity: 3.25
Hardness: 5 to 5½
Streak: Very pale blue
Colour: Cerulean blue
Solubility: Partly soluble in boiling concentrated hydrochloric acid
Environments:

Hydrothermal environments

Papagoite is a rare secondary mineral.

At the Messina mines, South Africa, papagoite occurs as inclusions in quartz associated with ajoite.

At the type locality, the New Cornelia mine, Ajo, Pima county, Arizona, USA, papagoite occurs in narrow veinlets in metasomatically altered granodiorite on a rock that consists chiefly of quartz and albite; associated with this assemblage are lesser amounts of sericite, epidote and calcite, and minor amounts of apatite, rutile, titanite, zircon, anatase and alunite; tenorite, aurichalcite, shattuckite, ajoite and baryte may also be present.

Common impurities: Fe,Mn,Ti,Mg,H2O

Paracelsian

Formula: Ba(Al2Si2O8)
Tectosilicate (framework silicate), feldspar group
Specific gravity: 3.29 to 3.32
Hardness: 5½ to 6
Streak: White
Colour: Colourless, white, pale yellow
Environments:

Metamorphic environments

At Candoglia, Italy paracelsian occurs as pale yellow granules in schist.
At the Benallt mine, Wales, UK, paracelsian is found in celsian in a band in shale and sandstone associated with a metamorphosed manganese deposit.

Common impurities: Fe,Mg,Ca,Na,K,H2O

Paragonite

Formula: NaAl2(Si3Al)O10(OH)2 phyllosilicate (sheet silicate), mica group, forms a series with muscovite.
Specific gravity: 2.78
Hardness: 2½
Streak: White
Colour: Colourless, pale yellow
Solubility: Insoluble in water and hydrochloric acid
Environments:

Sedimentary environments
Metamorphic environments

Paragonite is a metamorphic mineral formed under a broad range of pressure-temperature conditions, sometimes associated with kyanite and staurolite. It may also be found as detrital and authigenic (formed in place) sediments.
Paragonite is a common constituent of eclogite.
It is also found in phyllite, schist and gneiss.
It is a mineral of the greenschist and blueschist facies.

Alteration

amphibole, chlorite, paragonite, ilmenite, quartz and calcite to garnet, omphacite, rutile, H2O and CO2
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 + Mg5Al(AlSi3O10)(OH)8 + 3NaAl2(Si3Al)O10(OH)2 + 4Fe2+Ti4+O3 + 9SiO2 + 4CaCO3 → 2(CaMg2Fe3)Al4(SiO4)6 + 4NaCaMgAl(Si2O6)2 + 4TiO2 + 8H2O + 4CO2
In low-grade rocks relatively rich in calcite the garnet-omphacite association may be due to reactions such as the above.

lawsonite and jadeite to clinozoisite, paragonite, quartz and H2O
4CaAl2(Si2O7)(OH)2.H2O + NaAlSi2O6 ⇌ 2Ca2Al3[Si2o7][SiO4]O(OH) + NaAl2(Si3Al)O10(OH)2 + SiO2 +6H2
Clinozoisite and paragonite may have been derived from lawsonite by the above reaction.

Pargasite

Formula: NaCa2(Mg4Al)(Si6Al2)O22(OH)2 inosilicate (chain silicate) amphibole
Specific gravity: 3.069 to 3.181
Hardness: 5 to 6
Streak: White
Colour: Green, brown
Environments:

Metamorphic environments

Pargasite is a common component of skarn metamorphosed from siliceous limestone. It also may occur in schist and amphibolite.

Common impurities: Ti,Cr,Mn,K,F,H2O,P

Parisite

Formula:
Parisite-(Ce): CaCe2(CO3)3F2
Parisite-(La): CaLa2(CO3)3F2
Both are anhydrous carbonates containing halogen
Specific gravity: 4.33 to 4.39
Hardness:
Streak: Light yellow
Colour: Brown to yellow; colourless to yellow in transmitted light
Solubility: Soluble in hot strong acids
Environments:

Hydrothermal environments

Parisite is found in calcite veins in hydrothermal deposits

Paulingite

Paulingite is the name for two minerals
Paulingite-Ca: (Ca,K,Na,Ba,☐)10(Si,Al)42O84.34H2O
Paulingite-K: (K,Ca,Na,Ba,☐)10(Si,Al)42O84.34H2O
tectosilicates (framework silicates), zeolite group
Specific gravity: 2.10 to 2.22
Hardness: 5
Streak: White
Colour: Colourless, light yellow, orange, red
Environments:

Volcanic igneous environments

Paulingite occurs in basalt associated with erionite and pyrite.

Parnauite

Formula: Cu9(AsO4)2(SO4)(OH)10.7H2O
Compound arsenate
Specific gravity: 3.09
Hardness: 2
Streak: Pale green
Colour: Pale blue to green
Environments:

Hydrothermal environments

Parnauite is a rare secondary mineral.

At Cap Garonne mine, France, parnauite is associated with cyanotrichite, brochantite, lavendulan, mansfielditescorodite, chalcopyrite and cornubite.

At the Gwaithyrafon mine, Wales, UK, parnauite is associated with chrysocolla, brochantite, malachite, tyrolite and connellite.

At the type locality, Majuba Hill, Nevada, USA, parnauite occurs in the oxidised zone of a hydrothermal copper-tin orebody in rhyolite associated with spangolite, chalcophyllite, chenevixite, goudeyite, malachite, azurite, brochantite and chrysocolla.

Common impurities: P,C,Al

Pectolite

Formula: NaCa2Si3O8(OH) inosilicate (chain silicate) wollastonite group
Specific gravity: 2.8 to 2.9
Hardness: 4½ to 5
Streak: White
Colour: White, grey, sometimes greenish, yellowish, colourless
Solubility: Slightly soluble in hydrochloric acid
Environments:

Plutonic igneous environments
Basaltic cavities

Pectolite is a secondary mineral similar in occurrence to zeolites. It is found lining cavities in basalt, associated with zeolites, prehnite and calcite.

Periclase

Formula: MgO simple oxide
Specific gravity: 3.55 to 3.57
Hardness: 5½
Streak: White
Colour: Colourless, grayish white, yellow, brownish yellow, green, black
Solubility: Insoluble in water, soluble in hydrochloric, nitric and sulphuric acid
Environments:

Metamorphic environments

Periclase is found as a product of contact metamorphism of dolomite and magnesite.
It is a mineral of the amphibolite facies.

Alteration

During the progressive metamorphism of silica-rich dolostones the following approximate sequence of mineral formation is often found, beginning with the lowest temperature product: talc, tremolite, diopside, forsterite, wollastonite, periclase, monticellite

brucite to periclase and H2O
Mg(OH)2 ⇌ MgO + H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 840oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures (for the same pressure).

Common impurity: Fe

Perovskite

Formula: CaTiO3 simple oxide
Specific gravity: 3.98 to 4.26
Hardness: 5½
Streak: Colourless, greyish white
Colour: Dark brown, black, red-brown, yellow shades
Solubility: Insoluble in hydrochloric and nitric acids; slightly soluble in sulphuric acid
Environments:

Plutonic igneous environments
Carbonatites
Metamorphic environments

Perovskite is an accessory mineral in silica-poor rocks, such as nepheline syenite, kimberlite (common) and carbonatite. It also occurs in calcareous skarn.

Common impurities: Fe,Nb,Ce,La,TR

Petalite

Formula: LiAlSi4O10
Phyllosilicate (sheet silicate), feldspathoid
Specific gravity: 2.3 to 2.5
Hardness: 6 to 6½
Streak: White
Colour: Colourless, white, grey, pink
Solubility: Insoluble in acids
Environments:

Pegmatites

Petalite is found in granite pegmatites and related rocks, associated with spodumene, tourmaline, lepidolite, topaz, microcline, amblygonite, apatite, pollucite, columbite, cleavelandite and quartz.

Alteration

Petalite alters to montmorillonite.

petalite to spodumene and quartz
LiAlSi4O10 ⇌ LiAlSi2O6 + 2SiO2

Common impurities: Mg,Fe,Na,Ca,K,H2O

Pharmacosiderite

Formula: KFe3+4(AsO4)3(OH)4.6-7H2O
Specific gravity: 2.797
Hardness: 2½
Streak: White
Colour: Green, brown, yellow, red. Light brown in transmitted light.
Solubility: Soluble in hydrochloric acid. Green crystals immersed in ammonia turn red and revert to the original green colour when reimmersed in dilute hydrochloric acid.
Environments:

Hydrothermal environments

Pharmacosiderite is a secondary mineral occurring in the oxidised zones of iron-bearing sulphide deposits or in hydrothermal deposits. Pharmacosiderite alters to limonite and manganese oxides, and forms pseudomorphs after siderite.
Common impurities: P

Phenakite

Formula: Be2(SiO4) nesosilicate, phenakite group
Specific gravity: 2.98
Hardness: 7½ to 8
Streak: White
Colour: Colourless, white, yellow, pale rose
Solubility: Insoluble in acids
Environments:

Pegmatites
Sedimentary environments
Hydrothermal environments

Phenakite occurs in granite pegmatites with microcline, topaz and quartz, and also in schist as a product of beryl alteration. At Takovaya in the Russian Urals, phenakite occurs in schist with emerald and chrysoberyl.

Phillipsite

The phillipsite group is a group of tectosilicates (framework silicates) and a sub-group of the zeolite group, comprising:
Phillipsite-Ca: Ca3(Si10Al6)O32.12H2O
Phillipsite-K: K6(Si10Al6)O32.12H2O
Phillipsite-Na: Na6(Si10Al6)O32.12H2O
Phillipsite forms a series with harmotome
Specific gravity: 2.2
Hardness: 4 to 5
Streak: White
Colour: White
Solubility: Moderately soluble in hydrochloric acid
Environments:

Sedimentary environments
Hydrothermal environments
Basaltic cavities (most commonly)

Phillipsite is a common zeolite in basaltic cavities, ore veins, lithified rhyolitic vitric tuff (consolidated pyroclastic rock), saline lake deposits, and ocean floor sediments. It forms in Iceland in geothermal wells at 60 to 85oC
Phillipsite is a mineral of the zeolite facies

In the basaltic rocks near Kladno, Czechoslovakia, phillipsite is associated with thomsonite, mesolite, chabazite and natrolite, and it is always the first of these minerals to have been formed.

Phlogopite

Formula: KMg3(AlSi3O10)(OH)2 phyllosilicate (sheet silicate) mica group
Specific gravity: 2.78 to 2.85
Hardness: 2 to 3
Streak: White
Colour: Brown, gray, green, yellow, or reddish brown
Solubility: Slightly soluble in sulphuric acid
Environments:

Plutonic igneous environments
Carbonatites
Metamorphic environments

Phlogopite is found in metamorphosed Mg-rich limestone, dolostone and ultramafic rocks.

It is an essential constituent of kimberlite.
It also may be found in peridotite, dolostone and skarn.
At the Pyrites Mica mine, St Lawrence county, New York, USA, phlogopite often alters to clinochlore.

Alteration

almandine and phlogopite to pyrope and annite
Fe2+3Al2(SiO4)3 + KMg3AlSi3O12(OH)2 ⇌ Mg3Al2Si3O12 + KFe3AlSi3O10(OH)2
This assemblage is commonly formed during amphibolite facies metamorphism of pelitic rocks.

anorthite, enstatite, spinel, K2O and H2O to Al-rich hornblende, Mg-rich sapphirine and phlogopite
2.5Ca(Al2Si2O8) + 10MgSiO3 + 6MgAl2O4 + K2O + 3H2O → Ca2.5Mg4Al(Al2Si6)O22(OH)2 + 3Mg2Al4SiO10 + 2KMg3(AlSi3O10)(OH)2
This reaction occurs in the granulite to amphibolite facies.

antigorite and muscovite to phlogopite, amesite, SiO2 and H2O
5Mg3Si2O5(OH)4 + 3KAl2(AlSi3O10)(OH)2 → 3KMg3(AlSi3O10)(OH)2 + 3Mg2Al(AlSiO5)(OH)4 + 7SiO2 + 4H2O

dolomite, K-feldspar and H2O to phlogopite, calcite and CO2
3CaMg(CO3)2 + KAlSi3O8 + H2O = KMg3AlSi3O10(OH)2 + 3CaCO3 + 3CO2
In the presence of Al and K the metamorphism of dolomite leads to the formation of phlogopite according to the above equation.

Al-rich hornblende, spinel, quartz, K2O and H2O to anorthite, Mg-rich sapphirine and phlogopite
Ca2.5Mg4Al(Al2Si6)O22(OH)2 + 4 MgAl2O4 + 6SiO2 + K2O + H2O → 2.5Ca(Al2Si2O8) + Mg2Al4SiO10 + 2KMg3(AlSi3O10)(OH)2

phlogopite, calcite and quartz to diopside, microcline, H2O and CO2
KMg3(AlSi3O10)(OH)2 + 3CaCO3 + 6SiO2 = 3CaMgSi2O6 + K(AlSi3O8) + H2O + 3CO2
In reaction zones between interbedded carbonate and pelitic beds of the calc-mica schists, phlogopite may alter according to the above reaction.

Common impurities: Mn,Ba,Cr,Na,Ti,Ni,Zn,Ca,Li,Rb,H2O

Phosgenite

Formula: Pb2(CO3)Cl2 anhydrous carbonate containing halogen
Specific gravity:
Hardness: 2 to 3
Streak: White
Colour: Colourless, white, yellow, brown, greenish or pink; colourless in transmitted light
Solubility: Moderately soluble in nitric acid with effervescence. Decomposed slowly in cold water, which extracts lead chloride
Environments:

Hydrothermal environments

Phosgenite is a secondary mineral found in the weathered zone of lead ore deposits. It readily alters to, and is replaced by, cerussite

Phoenicochroite

Formula: Pb2(CrO4)
Specific gravity: 7.01
Hardness: 2½
Streak: Brick red
Colour: Dark red
Solubility: Soluble in hydrochloric acid with separation of lead chloride
Environments:

Hydrothermal environments

Phoenicochroite is a rare secondary mineral in the oxidised zone of chromium-bearing hydrothermal lead deposits, associated with crocoite, vauquelinite, fornacite, hemihedrite, iranite, pyromorphite, mimetite, cerussite, leadhillite, galena, calcite, fluorite and quartz.
Phoenicochroite superficially alters to crocoite which is then replaced by cerussite, mimetite and vauquelinite.

At the type locality, the Berezovsk Mines, Ural mountains, Russia, phoenicochroite is associated with vauquelinite, pyromorphite, galena, crocoite and anglesite.

At various localities in Arizona, USA, phoenicochroite occurs with mimetite, willemite, hemihedrite and vauquelinite.

Pirssonite

Formula: Na2Ca(CO3)2.2H2O hydrated normal carbonate
Specific gravity: 2.352
Hardness: 3 to 3½
Streak: White
Colour: Colourless, white, greyish
Solubility: Soluble in cold dilute acids with effervescence
Environments

Sedimentary environments

Pirssonite is an evaporite mineral.

Localities

Namibia

At the Otjiwalundo Salt Pan, Kunene Region, pirssonite occurs with trona and thénardite.

USA

At Borax Lake, California, pirssonite occurs with northupite, tychite and gaylussite.

Near Green River, Wyoming, it has been recovered from drill cores with shortite, bradleyite, northupite, gaylussite and trona.

Plagioclase

Plagioclase feldspars form a continuous series of tectosilicates (framework silicates) from
anorthite CaAl2Si2O8 to
albite NaAlSi3O8. They include oligoclase (10 to 30% anorthite), andesine (30 to 50% anorthite), labradorite (50 to 70% anorthite) and bytownite (70 to 90% anorthite), as well as the end members.
Environments:

Plutonic igneous environments
Volcanic igneous environments
Metamorphic environments

The plagioclase feldspars are widely distributed as rock-forming minerals, and more abundant than the K-feldspars. They are minerals of the granulite facies. Plagioclase is an essential constituent of diorite, rhyolite, andesite and basalt.
It is a common constituent of quartzolite and also may be found in granite.
It is a mineral of the hornblende-hornfels, pyroxene-hornfels, amphibolite and granulite facies.

Plancheite

Formula: Cu8(Si4O11)2(OH)4.H2O
Inosilicate (chain silicate)
Specific gravity: 3.4
Hardness: 5
Streak: Light blue
Colour: Pale to dark blue
Environments:

Hydrothermal environments

Plancheite is a rare secondary mineral in the oxidised portion of copper deposits, associated with chrysocolla, dioptase, malachite, conichalcite and tenorite.

At Table mountain mine, Pinal county, Arizona, USA, plancheite occurs with compact conichalcite.

Platinum

Formula: Pt native element
Specific gravity: 21.4
Hardness: 4 to 4½;
Streak: Grey
Colour: Silver grey
Solubility: Insoluble in hydrochloric,