Bertrandite from the Golconda pegmatite, Minas Gerais, Brazil
Category Sorosilicate
(repeating unit)
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
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°
References [1][2][3]

Bertrandite is a beryllium sorosilicate hydroxide mineral with composition: Be4Si2O7(OH)2. Bertrandite is a colorless to pale yellow orthorhombic mineral with a hardness of 6-7.

It is commonly found in beryllium rich pegmatites and is in part an alteration of beryl. Bertrandite often occurs as a pseudomorphic replacement of beryl. Associated minerals include beryl, phenakite, herderite, tourmaline, muscovite, fluorite and quartz.[1]

It, with beryl, are ores of beryllium.

It was discovered near Nantes, France in 1883 and named after French mineralogist, Emile Bertrand (1844–1909).[1][2][3]

See also


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