Mineral - Bertrandite
Bertrandite
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
Be₄(Si₂O₇)(OH)₂
Unit Cell
a=8.72 b=15.27 c=4.57 Z=4
Physical Properties
Hardness
6 - 7
Streak
white
Density
Normal (2-3,5)
Cleavage
Perfect after {001}, distinct after {100}, {010}, {110}
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
whitecolorless
Birefringence
0.023
Luster
Vitreous,
Pearly
Transparency
translucent,
transparent
Pleochroism
Geomineralogical Properties
Crystal System
orthorhombic
Point Group
orthorhombic-pyramidal - mm2
Space Group
Cmc2 1 (36)
Habit
blocky, acicular, prismatic, radial, tabular
Formation
Secondary, through the hydrothermal alteration of Beryl in granitic, miarolitic cavities
Paragenesis
Twinning
After {011} or {021}, as heart-shaped, V-shaped or Y-shaped twins
Rarity
Rather rare
Synonyms
Bertrandite, Hessenbergite
Composition
Elements
Mass
SiO₂
49.26
Al₂O₃
0.01
Fe₂O₃
1.40
BeO
42.00
H₂O
6.90
France (Dana 1892)