Bertrandite

sorosilicate

beryl

Formula: Be4Si2O7(OH)2
Sorosilicate
Specific gravity: 2.59 to 2.6
Hardness: 6 to 7
Streak: White
Colour: Colourless, pale yellow
Solubility: Soluble in hydrogen fluoride, HF, sulphuric acid and sodium hydroxide. Partially soluble in hydrochloric acid (Dana).
Environments:

Plutonic Igneous Environments
Pegmatites typical
Metamorphic Environments
Hydrothermal Environments

Bertrandite is commonly found in beryllium-bearing pegmatites, (Webmin). and also in fissures in granite and in miarolitic cavities in greisen. It is commonly an alteration product of beryl, more rarely a primary mineral. Associated minerals include beryl, phenakite, herderite, tourmaline, muscovite, fluorite and quartz (HOM).

It may also occur in hydrothermal veins as a late-stage product of beryl resorption and alteration, and it may form pseudomorphs after beryl (Dana).

At Mica creek, Queensland, Australia, bertrandite occurs in a beryl-bearing pegmatite, associated with beryl, mica, quartz, albite and limonite. Most of the bertrandite shows marginal replacement by mica (AM45.1300).

There are two type localities, Barbin quarry and Petit-Port, , both at Nantes, Pays de la Loire, France.

At the Tae Hwa mine, Chung Cheong North Province, South Korea, bertrandite occurs in vein deposits associated with beryl, scheelite, wolframite (mineral intermediate between hübnerite and ferberite) and dolomite (Dana).

At Spitkopje, Erongo Region, Namibia, bertrandite occurs in a pegmatite, where it is the last beryllium-bearing mineral to crystallise (MinRec 36.4.323).

At Mount Antero, Chaffee county, Colorado, USA, bertrandite is associated with beryl and phenakite (Dana).

At Folsom Gulch, Carroll County, New Hampshire, USA, bertrandite occurs on microcline (R&M 93.2.161).

Alteration

bertrandite to phenakite and H2O
Be4Si2O7(OH)2 ⇌ 2Be2(SiO4) + H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

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).

bertrandite, kaolinite and quartz to beryl and H2O
3Be4Si2O7(OH)2 + 4Al2Si2O5(OH)4 + 10SiO2 ⇌ 4Be3Al2Si6O18 + 11H2O
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).

Common impurities: Al,Fe,Ca

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