Mineral - Topaz
Topaz
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
Al₂(SiO₄)(F,OH)₂
Unit Cell
a=4.65 b=8.80 c=8.39 Z=4
Physical Properties
Hardness
8
Streak
white
Density
Normal (2-3,5)
Cleavage
Perfect after {001}
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
brownredorangeyellowbluecolorless
Birefringence
0.010
Luster
Vitreous
Transparency
translucent,
transparent
Pleochroism
Geomineralogical Properties
Crystal System
orthorhombic
Point Group
orthorhombic-dipyramidal - 2/m 2/m 2/m
Space Group
Pnma (62)
Habit
blocky, granular, prismatic, columnar, tabular
Formation
Pneumatolytic to hydrothermal, resulting from the interaction of fluoride-bearing fluid phases with acidic magmatic rocks, particularly in greisen, pegmatites, and pneumatolytic veins, as a consequence of fluid enrichment during the late magmatic phase.
Paragenesis
Twinning
Rarity
Common
Synonyms
Topaz
Composition
Elements
Mass
SiO₂
31.93
Al₂O₃
56.26
F
20.37
H₂O
0.19
O=F₂
8.58
Utah (Dana 1895)