Euclase

beryllium

bertrandite

Formula: BeAlSiO4(OH)
Nesosilicate (insular SiO4 groups), beryllium mineral
Specific gravity: 2.99 to 3.10
Hardness: 7½
Streak: White
Colour: Colourless, white, pale green to deep yellowish green, greenish blue, pale blue to deep blue
Solubility: Insoluble in acids
Environments:

Pegmatites
Metamorphic environments
Hydrothermal environments

Euclase is a low-temperature hydrothermal mineral in granite pegmatites and Alpine veins. It is also found in chlorite schist and phyllite, and as a detrital mineral (Dana). In pegmatites it is a product of decomposition of beryl (HOM). Associated minerals include feldspar, quartz, topaz, beryl, mica, calcite, ankerite and chlorite (HOM).

The type locality is Ouro Preto, Minas Gerais, Brazil.

Alteration

Euclase is stable over a broad rangeof pressure and temperature, but it is stable only in environments with unusually high alumina activities, thus accounting for its relative rarity (AM 71.277-300).

bertrandite, euclase and quartz to beryl and H2O
Be4Si2O7(OH)2 + 8BeAlSiO4(OH) + 14SiO2 ⇌ 4Be3Al2Si6O18 + 5H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

bertrandite and kaolinite to euclase, beryl and H2O
4Be4Si2O7(OH)2 + 7Al2Si2O5(OH)4 ⇌ 10BeAlSiO4(OH) + 2Be3Al2Si6O18 + 13H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

bertrandite and kaolinite to euclase, quartz and H2O
Be4Si2O7(OH)2 + 2Al2Si2O5(OH)4 ⇌ 4BeAlSiO4(OH) + 2SiO2 + 3H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

chrysoberyl, bertrandite and kaolinite to euclase and H2O
2BeAl2O4 + 2Be4Si2O7(OH)2 + 3Al2Si2O5(OH)4 ⇌ 10BeAlSiO4(OH) + 3H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

euclase to bertrandite, chrysoberyl, quartz and H2O
8BeAlSiO4(OH) ⇌ Be4Si2O7(OH)2 + 4BeAl2O4 + 6SiO2 + 3H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

euclase to beryl, chrysoberyl, phenakite and H2O
20Eu to 3Be3Al2Si6O18 + 7BeAl2O4 + 2Be2(SiO4) + 10H2O
Increasing temperature and decreasing pressure favours the forward reaction. At a pressure of 6 kbar the equilibrium temperature is about 500oC, in the absence of impurities which might be incorporated in the beryl (AM 71.277-300).

euclase to phenakite, chrysoberyl, beryl and H2O
20BeAlSiO4(OH) ⇌ 2Be2(SiO4) + 7BeAl2O4 + 3Be3Al2Si6O18 + 10H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

euclase and kaolinite to chrysoberyl, quartz and H2O
2BeAlSiO4(OH) + Al2Si2O5(OH)4 ⇌ 2BeAl2O4 + 4SiO2 + 3H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

euclase and silica to beryl, chrysoberyl and H2O
4Eu + 2SiO2 to Be3Al2Si6O18 + BeAl2O4 + 2H2O
Increasing temperature and decreasing pressure favours the forward reaction. At a pressure of 8 kbar the equilibrium temperature is about 500oC, in the absence of impurities which might be incorporated in the beryl (AM 71.277-300).

euclase and quartz to beryl, kaolinite and H2O
6BeAlSiO4(OH) + 8SiO2 ⇌ 2Be3Al2Si6O18 + Al2Si2O5(OH)4 + H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

euclase and quartz to chrysoberyl, beryl and H2O
4BeAlSiO4(OH) + 2SiO2 ⇌ BeAl2O4 + Be3Al2Si6O18 + 2H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

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

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