Albite

albite

tschermakite

plagioclase

andesine

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Formula: Na(AlSi3O8)
Tectosilicate (framework silicate), plagioclase feldspar, feldspar group, forms a series with anorthite

Varieties

Andesine is a variety of albite with an albite:
anorthite molar ratio ranging from 50 : 50 to 70 : 30. It is 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.
Pericline is a variety of albite occurring as milky-white, elongated crystals.

Properties

Crystal System: Triclinic
Specific gravity: 2.6 to 2.65 measured, 2.615 calculated
Hardness: 6 to 6½
Streak: White
Colour: Colourless, white
Luminescence: Fluorescent red, very weak. Most common activator: Fe3+ (FM)
Melting point: About 1,100oC at atmospheric pressure
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Common impurities: Ca,K,Mg
Environments:

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 (AofA).
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 aegirine 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
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 (JVW p143 & KB p209).

Localities

At the Mud Tank Zircon Field, Alcoota Station, Central Desert Region, Northern Territory, Australia, white chunks of albite occasionally occur in the gravels. There is also a pale blue transparent moonstone that owes its colour to minute magnetite inclusions (Minrec 51.6.815-824).

At the Sapo mine, Minas Gerais, Brazil, albite is abundant in the pegmatite, associated with microcline, especially in large, quartz-bearing cavities. It is mostly of the cleavelandite variety, often intergrown with muscovite with hollow voids whhich may be moulds of dissolved spodumene crystals (Min Rec 40.4.278).

The Mponeng Mine, West Wits, Far West Rand, West Rand District Municipality, Gauteng, South Africa, is a gold mine and the deepest mine on Earth. Here aggregates of white, transparent to translucent crystals of albite to 12 mm have been collected, associated with pyrrhotite and quartz. Apart from these discoveries albite crystals are exceedingly rare at the Witwatersrand goldfield (R&M 96.4.318).

At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, albite variety cleavelandite occurs associated with phosphate pods, niobium/tantalum oxides and pollucite. The Emmons pegmatite is an example of a highly evolved boron-lithium-cesium-tantalum enriched pegmatite (R&M 94.6.503).

At the Little Gem amethyst mine, Jefferson county, Montana, USA, albite occurs intergrown with microcline (R&M 93.6.512)

At the Keyes Mica Quarries, Orange, Grafton County, New Hampshire, USA, the pegmatites are beryl-type rare-element (RE) pegmatites.
The Number 1 mine exposed a pegmatite that shows the most complex zonation and diverse mineralogy of any of the Keyes pegmatites. Six zones are distinguished, as follows, proceeding inward from the margins of the pegmatite:
(1) quartz-muscovite-plagioclase border zone, 2.5 to 30.5 cm thick
(2) plagioclase-quartz-muscovite wall zone, 0.3 to 2.4 metres thick
(3) plagioclase-quartz-perthite-biotite outer intermediate zone, 0.3 to 5.2 metres thick, with lesser muscovite
(4) quartz-plagioclase-muscovite middle intermediate zone, 15.2 to 61.0 cm thick
(5) perthite-quartz inner intermediate zone, 0.9 to 4.6 meters thick
(6) quartz core, 1.5 to 3.0 metres across
The inner and outer intermediate zones contained perthite crystals up to 1.2 meters in size that were altered to vuggy albite-muscovite with fluorapatite crystals. This unit presumably was the source of the albite, muscovite, fluorapatite, quartz and other crystallised minerals found in pieces of vuggy albite rock on the dumps next to the mine.
The middle intermediate zone produced sheet mica with accessory minerals including tourmaline, graftonite, triphylite, vivianite, pyrite, pyrrhotite, and beryl crystals to 30.5 cm long and 12.7 cm across.
Albite occurs in all the Keyes pegmatites. It locally replaced perthite, forming a vuggy rock with excellent crystals of albite to several centimetres. Associated minerals in the vuggy albite suite include well-crystallised fluorapatite, muscovite, quartz and schorl. Less commonly, hydroxylherderite, pyrite, siderite and other minerals occur in this suite (R&M 97.4.310).

The Purple Diopside Mound, Rose Road, Pitcairn, St. Lawrence county, New York, USA, is situated in marble. The development of veins of large crystals probably occurred as a result of fluid penetration from a concurrent intrusion. Many of the minerals of interest to collectors formed during this primary event, with additional species resulting from the subsequent alteration of scapolite. There seems to be little, if any, secondary, late-stage mineralisation present.
Albite occurs sparingly as small, white, tabular crystals to 2 cm and patches in massive purple diopside (R&M 96.6.548). It fluoresces deep rose-pink under short wave UV (R&M 97.5.334-344).

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 (DHZ 2A p511)

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 (DHZ 2A p651)

albite to nepheline and quartz
Na(AlSi3O8) ⇌ NaAlSiO4 + 2SiO2
(JVW p143)

albite and NaCl (aqueous) to sodalite and silica
6Na(AlSi3O8) + 2NaCl → 2Na4(Si3Al3)O12Cl + 12SiO2 (http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.613.9474&rep=rep1&type=pdf)

albite, chlorite and calcite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz, CO2 and H2O
8Na(AlSi3O8) + (Mg4.0Fe2.0)(AlSi3O10)(OH)8 + CaCO3 → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 2SiO2 + CO2 + 2H2O
In low to intermediate metamorphism jadeite-glaucophane assemblages may arise from reactions such as the one above (DHZ 2A p475).

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 (DHZ 2A p512).

albite and montmorillonite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz and H2O
8Na(AlSi3O8) + 2Ca0.5(Mg3.5Al0.5)Si8O20(OH)4.nH2O → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 15SiO2 + 6H2O
This reaction occurs in low to intermediate metatmorphism (DHZ 2A p 475).

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 (DHZ 2A p453).

analcime and quartz to albite and H2O
Na(AlSi2O6).H2O + SiO2 ⇌ Na(AlSi3O8) + H2O (JVW p144)

anorthite, albite and H2O to jadeite, lawsonite and quartz
CaAl2 Si2O8 + NaAlSi3O8 + 2H2O → NaAlSi2O6 + CaAl2(Si2O7)(OH)2.H2 + SiO2 (DHZ 2A p475)

antigorite and albite to glaucophane and H2O
Mg3Si2O5(OH)4 + 2Na(AlSi3O8) → ☐Na2(Mg3Al2)Si8O22(OH)2 + H2O
This is a metamorphic reaction (DHZ 3 p156).

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 (DHZ 2A p449).

chlorite (clinichlore), actinolite and albite to glaucophane, iron-poor epidote, SiO2 and H2O
9Mg5Al(AlSi3O10)(OH)8 + 6☐Ca2Mg5Si8O22(OH)2 + 50Na(AlSi3O8) → 25☐Na2(Mg3Al2)Si8O22(OH)2 + 6Ca2Al3[Si2O7][SiO4]O(OH) + 7SiO2 + 14H2O
This is a metamorphic reaction (DHZ 3 p156).

diopside and albite to omphacite and quartz
CaMgSi2O6 + xNaAlSi3O8 ⇌ CaMgSi2O6.xNaAlSi2O6 + SiO2 (DHZ 2A p453).

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 (DHZ 2A p139)

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 (DHZ 2A p139).

jadeite to nepheline and albite
2NaAlSi2O6 ⇌ NaAlSiO4 + NaAlSi3O8
At 20 kbar pressure the equilibrium temperature is about 1,000oC (eclogite facies), with equilibrium to the right at higher temperatures and to the left at lower temperatures (Minsoc Amer sp pap 2, 151-161 (1969)).

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

labradorite (variety of anorthite), 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 (DHZ 2A p449).

nepheline and diopside to åkermanite, forsterite and albite
3NaAlSiO4 + 8CaMgSi2O6 ⇌ 4Ca2MgSi2O7 + 2Mg2SiO4 + 3NaAlSi3O8
This reaction is in equilibrium at about 1180oC, with lower temperatures favouring the forward reaction (DHZ 4 p251).

paragonite and quartz to albite and andalusite and H2O
NaAl2(Si3Al)O10(OH)2 + SiO2 ⇌ Na(AlSi3O8) + Al2OSiO4 + H2O
Increasing temperature favours the forward reaction (AM61.699-709).

paragonite and quartz to albite, kyanite and H2O
NaAl2(Si3Al)O10(OH)2 + SiO2 ⇌ Na(AlSi3O8) + Al2OSiO4 + H2O
Increasing temperature favours the forward reaction (AM61.699-709).

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 (AM 67.97-113).

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 (AM 67.97-113).

magnesium-rich tremolite, tschermakite and albite to pargasite and quartz
☐Ca2Mg5Si8O22(OH)2 + ☐Ca2(Mg3Al2)(Si6Al2)O22(OH)2 + 2Na(AlSi3O8) ⇌ 2NaCa2(Mg4Al)(Si6Al2)O22(OH)2 + 8SiO2
(AM 92.4.491)

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