Mineral - Phenakite
Phenakite
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
Be₂[SiO₄]
Unit Cell
a=12.47 c=8.25 Z=18
Physical Properties
Hardness
7.5 - 8
Streak
white
Density
Normal (2-3,5)
Cleavage
Distinct after {11 2 0}, imperfect after {10 1 1}
Fracture
conchoidal
Tenacity
Brittle
Optical Properties
Color
whiteyellowpinkcolorless
Birefringence
0.017
Luster
Vitreous,
Greasy
Transparency
transparent
Pleochroism
Geomineralogical Properties
Crystal System
trigonal
Point Group
rhombohedral - 3
Space Group
R 3 (148)
Habit
granular, prismatic, tabular, barrel-shaped
Formation
(1) Primary magmatic in highly differentiated, beryllium-rich granitic pegmatites or aplites, often under hydrothermal conditions.
(2) Metasomatic at the contact zones between beryllium-bearing intrusions and aluminum-rich surrounding rocks (e.g., mica schists)
Paragenesis
Twinning
Drill-shaped penetration twins after {0001}
Rarity
Rarely
Synonyms
Phenakite
Composition
Elements
Mass
SiO₂
52.92
Al₂O₃
0.01
BeO
45.82
MgO
0.13
CaO
0.20
Na₂O
0.63
K₂O
0.26
0.21
Russia (Dana 1895)
Groups and Members
Phenakite-Group