Minerals

A: acanthite, actinolite, adamite, adularia (variety of orthoclase), aegirine, aenigmatite, agardite, ajoite, åkermanite, 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, 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, chondrodite, chromite, chrysoberyl, chrysocolla, chrysotile, cinnabar, cleavelandite (variety of albite), clinochlore (variety of chlorite), clinoenstatite, clinohedrite, clinohumite, clinoptilolite, clinozoisite, coesite, colemanite, columbite, conichalcite, cookeite, copper, cordierite, corkite, coronadite, corundum, covellite, crandallite, cristobalite, crocoite, cronstedtite, cubanite, cummingtonite, cuprite, cyanotrichite
D: dachiardite, danburite, datolite, dawsonite, descloizite, 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, garnet, garronite, gaylussite, gedrite, gehlenite, gibbsite, 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, hildagoite, hollandite, hornblende, hübnerite, humite, hyalophane (variety of microcline), hydrocerussite, hypersthene
I: illite (variety of muscovite), ilmenite, imogolite
J: jacobsite, jadeite, jarosite, johannsenite
K: K-feldspar, kalsilite, kaolinite, kegelite, kernite, kinoite, kintoreite, kolbeckite, kyanite
L: labradorite (variety of anorthite), laumontite, lawsonite, lead, leadhillite, lepidocrocite, lepidolite, leucite, leucophanite, lévyne, linarite, lindqvistite, litharge, luddenite
M: magnesioferrite, magnesite, magnetite, magnetoplumbite, malachite, manganite, manganosite, mansfieldite, marcasite, margarite, massicot, mawbyite, mazzite, melanotekite, melanterite, melilite, mendipite, merlinoite, merwinite, mesolite, metatorbernite, metavariscite, mica, microcline, millerite, millisite, mimetite, minium, mirabilite, 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, orpiment, orthoclase, overite
P: paragonite, pargasite, paulingite, parnauite, pectolite, periclase, perovskite, petalite, pharmacosiderite, phenakite, phillipsite, phlogopite, phoenicochroite, pirssonite, plagioclase feldspar, plancheite, platinum, plumboferrite, pollucite, prehnite, proustite, pseudobrookite, psilomelane, pumpellyite, pyrargyrite, pyrite, pyrochlore, pyrolusite, pyromorphite, pyrope, pyrophyllite, pyroxene, pyroxmangite, pyrrhotite
Q: quartz
R: ranciéite, realgar, red beryl (variety of beryl), rhodochrosite, rhodonite, riebeckite, rutile
S: sanidine, sapphirine, scapolite, schairerite, scheelite, schorl, scolecite, scorodite, searlesite, segnitite sellaite, sericite (variety of muscovite), serpentine, shattuckite, shortite, siderite, sillimanite, silver, smithsonite, sodalite, spangolite, spessartine, sphalerite, spinel, spodumene, spurrite, staurolite, stephanite, stibnite, stilbite, stilpnomelane, stishovite, strontianite, sulphohalite, sulphur, svabite, sylvanite, sylvite
T: talc, tantalite, 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(Mg_4.5-2.5Fe²⁺_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 280^oC.
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

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: 1,454^oC 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 1345^oC, when the stable mixture is åkermanite and wollastonite. From 1240^oC down to 1050^oC 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 1,050^oC.

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 890^oC (granulite facies).

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

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 1,100^oC 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) + (Mg_4.0Fe_2.0)(AlSi₃O₁₀)(OH)₈ + CaCO₃ → 5(Na_0.8Ca_0.2)(Mg_0.2Al_0.8Si₂)₆ + 2Na₂(Mg₃Al₂)(Al_0.5Si_7.5)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) + 2Ca_0.5(Mg_3.5Al_0.5)Si₈O₂₀(OH)₄.nH₂O → 5(Na_0.8Ca_0.2)(Mg_0.2Al_0.8Si₂)₆ + 2Na₂(Mg₃Al₂)(Al_0.5Si_7.5)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 1,000^oC (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
High pressure favours the reverse reaction.
The equilibrium temperature for this reaction at 10 kbar pressure is about 400^oC (blueschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

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.

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

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 also in manganese 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 +/- 40^oC, 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(Mg_4.5-2.5Fe²⁺_0.5-2.5Si₈O₂₂(OH)₂ ☐Ca₂(Mg_4.5-2.5Fe²⁺_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(Mg_5.0-4.5Fe²⁺_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
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 600^oC and 640^oC, and pressure between 5 and 13 kbar, in associations with prehnite, calcite and zeolites. 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 60^oC to 300^oC 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.

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

Andalusite, sillimanite and kyanite are polymorphs (same formula, different structure); they are in equilibrium at a pressure of 3.75 kbar and temperature 504^oC (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 320^oC (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 320^oC (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 440^oC (greenschist facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures.

muscovite and quartz to andalusite, K-feldspar and H₂O
KAl₂(Si₃Al)O₁₀(OH)₂ + SiO₂ ⇌ Al₂SiO₅ + KAlSi₃O₈ + H₂O
At 1 kbar pressure the equilibrium temperature is about 550^oC (hornblende-hornfels facies)

pyrophyllite to andalusite, quartz and H₂O
Al₂Si₄O₁₀(OH)₂ ⇌ Al₂SiO₅ + 3SiO₂ + H₂O
The equilibrium temperature for this reaction at 1.8 kbar pressure is 414^oC (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(Mg0.5Fe_0.5)(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 1,550^oC 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, 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.

anorthite, H₂SO₄ and H₂ 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, enstatite, spinel, K₂O and H₂O to Al-rich hornblende, Mg-rich sapphirine and phlogopite
2.5Ca(Al₂Si₂O₈) + 10MgSiO₃ + 6MgAl₂O₄ + K₂O + 3H₂O → Ca_2.5Mg₄Al(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 1,110^oC (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 950^oC At 4.3 kbar pressure the equilibrium temperature is about 890^oC (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 540^oC (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 510^o (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 540^oC (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 510^o (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 730^oC (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
Ca_2.5Mg₄Al(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 480^oC (greenschist facies), and at 10 kbar it is about 720^oC (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 520^oC (amphibolite facies), and at 9 kbar it is about 675^oC (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 610^oC (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 440^oC (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 520^oC (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 760^oC, and at 10 kbar it is about 950^oC (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 650^oC (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 690^oC (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 540^oC (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 (retrograde metamorphism refers to changes that occur during uplift and cooling of a rock) 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 810^oC (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 690^oC (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 650^oC (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 790^oC (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 750^oC 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 600^oC (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 500^oC (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 450^oC (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 580^oC (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 (decreasing metamorphic grade) 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 400^oC, 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, romanechite 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 1,000^oC.

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

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: Ba_0.5Fe³⁺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 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 300^oC. At low salinities baryte becomes more soluble (retrograde solubility) above about 100^oC.

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 Ca₄Be_2+xAl_2-xSi₉O_26-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 dusserite.

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 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 and gneiss.
It also may be found in 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.

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: 434^oC

Hydrothermal environments

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

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 840^oC (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 450^oC (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:

In manganese ores formed by metamorphism of manganese-bearing sediments with attendant metasomatism. Type locality - Carbonate-silicate hosted zinc deposit Bustamite typically results from metamorphism of manganese-bearing sediments. At Franklin, New Jersey, the oldest rocks are Precambrian gneisses of mixed sedimentary and volcanic origin. Franklin Marble was deposited within these rocks, along with sediments containing zinc, manganese and iron minerals. These sediments were metamorphosed later in the Precambrian, then the rocks were uplifted from the late Precambrian into the Cambrian and quartzite was deposited on the eroded surface. In Cambrian-Ordovician time the quartzite was in turn overlain by limestone, and the rocks have been subject to uplift and erosion up to the present time.
Common associates: 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

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) + (Mg_4.0Fe_2.0)(AlSi₃O₁₀)(OH)₈ + CaCO₃ → 5(Na_0.8Ca_0.2)(Mg_0.2Al_0.8Si₂)₆ + 2Na₂(Mg₃Al₂)(Al_0.5Si_7.5)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 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.

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 500^oC (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(Mg0.5Fe_0.5)(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 150^oC and 250^oC.

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 600^oC.

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.

monticellite and CO₂ to åkermanite, forsterite and calcite
3CaMgSiO₄ + CO₂ ⇌ Ca₂MgSi₂₇ + Mg₂O₇ + CaCO₃
At 4.3 kbar pressure the equilibrium temperature is about 890^oC (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 1,070^oC (granulite facies).

talc and calcite to dolomite and quartz
talc + calcite + CO₂ ⇌ dolomite + 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 250^oC and 450^oC.

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 450^oC and 600^oC.

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
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 300^oC.

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

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 CO₃^2- 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 + 3HAsO₄^2- + Cl^- + 4H⁺ ⇌ Pb₅(AsO₄)₃Cl + 5H₂CO₃
cerussite and mimetite can co-exist only under basic conditions at rather high P_CO2.

Chabazite

The chabazite series comprises five mineral species:
Chabazite-Ca: Ca₂[Al₄Si₈O₂₄]. 13H₂O
Chabazite-K: (K₂NaCa_0.5)[Al₄Si₈ O₂₄].11H₂O
Chabazite-Mg: (Mg_0.7K_0.5 Na_0.1)[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, usually with other zeolites, in cavities in basalt and 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 55^oC to 75^oC 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 Ca₃(Si₁₂Al₆)O₃₆.18H₂O/offretite KCaMg(Si₁₃Al₅)O₃₆.15H₂O, 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 the K-feldspar anorthoclase (Na,K)AlSi₃O₈.
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.
At Palabora, South Africa, chabazite-Ca is found associated with analcime, fluorapophyllite and heulandite.

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

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
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.

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) + (Mg_4.0Fe_2.0)(AlSi₃O₁₀)(OH)₈ + CaCO₃ → 5(Na_0.8Ca_0.2)(Mg_0.2Al_0.8Si₂)₆ + 2Na₂(Mg₃Al₂)(Al_0.5Si_7.5)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