Bertrandite is a rare mineral that forms small flattened or wedge-shaped prismatic crystals. It is also found in the form of continuous masses or radial-radiant splices. Often found in rare earth deposits Bertrandite is characterized by impurities of boron and germanium. Mined as an ore for beryllium. Named after the French mineralogist E. Bertrand.
You can see bertrandite stone for sale and buy it in the Minerals of Russia online store.
General | |
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Category | Sorosilicate |
Formula (repeating unit) |
Be4Si2O7(OH)2 |
IMA symbol | Btd |
Strunz classification | 9.BD.05 |
Crystal system | Orthorhombic |
Crystal class | Pyramidal (mm2) H-M symbol: (mm2) |
Space group | Ccm21 |
Unit cell | a = 8.7135(4) Å, b = 15.268(1) Å, c = 4.5683(3) Å; Z = 4 |
Identification | |
Color | Colorless to pale yellow |
Crystal habit | Thin tabular, prismatic to needle-like crystals commonly in radial clusters |
Twinning | Common on {011} or {021} forming heart or V shaped twins |
Cleavage | Perfect on {001}; distinct on {100}, {010} and {110} |
Mohs scale hardness | 6 - 7 |
Luster | Vitreous, pearly on cleavage surfaces |
Diaphaneity | Transparent |
Specific gravity | 2.59 - 2.60 |
Optical properties | Biaxial (-) |
Refractive index | nα = 1.591 nβ = 1.605 nγ = 1.614 |
Birefringence | δ = 0.023 |
2V angle | Measured: 73° to 81° |