Bertrandite

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Nevada, USA
21.60 carats
© Giovanni Scapin 2015

Bertrandite is named after Emile Bertrand, mineralogist and mining engineer of Paris, France, who first called attention to the mineral.

Bertrandite forms transparent, colourless to pale yellow crystals. Large and clean enough crystals suitable for faceting are rare.

Bertrandite often occurs as a pseudomorphic replacement of beryl.
General Information
Chemical Formula
Be
 
4
Si
 
2
O
 
7
(OH)
 
2
Anthony et al, Handbook of mineralogy (2001)
Photos of natural/un-cut material from mindat.org
Physical Properties of Bertrandite
Mohs Hardness6 to 7
Anthony et al, Handbook of mineralogy (2001)
Specific Gravity2.59 to 2.60
Anthony et al, Handbook of mineralogy (2001)
Cleavage QualityPerfect,Distinct
Anthony et al, Handbook of mineralogy (2001)
Optical Properties of Bertrandite
Refractive Index1.583 to 1.614
Anthony et al, Handbook of mineralogy (2001)
Optical CharacterBiaxial/-
Anthony et al, Handbook of mineralogy (2001)
DispersionWeak
Anthony et al, Handbook of mineralogy (2001)
Colour
Colour (General)Colorless to slightly yellow
Anthony et al, Handbook of mineralogy (2001)
TransparencyTransparent
Anthony et al, Handbook of mineralogy (2001)
LustreVitreous,Pearly
Anthony et al, Handbook of mineralogy (2001)
Crystallography of Bertrandite
Crystal SystemOrthorhombic
Anthony et al, Handbook of mineralogy (2001)
HabitCrystals thin tabular, commonly prismatic to needlelike, to 5 cm; in radial aggregates.
Anthony et al, Handbook of mineralogy (2001)
Geological Environment
Where found:In fissures in granites and associated pegmatites and in miarolitic cavities in greisens; commonly an alteration product of beryl, more rarely as a primary mineral.
Anthony et al, Handbook of mineralogy (2001)
Further Information
Mineral information:Bertrandite information at mindat.org
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