Chrysoberyl

oxide

beryllium mineral

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

Pegmatites
Metamorphic environments
Hydrothermal environments

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

At Carnaiba, Brazil, chrysoberyl variety alexandrite occurs in schist associated with emerald (Dana).

Near St Gothard, Switzerland, chrysoberyl occurs in dolostone with corundum (Dana).

At many localities in Maine, USA, chrysoberyl occurs with columbite, tourmaline, gahnite and beryl (Dana).

Alteration

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

Common impurities: Fe,Cr,Ti

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