Aluminium Hydroxy Flouro Silicate
Al2[(F,OH)2SiO4]
Chemical name
Aluminium Hydroxy Flouro Silicate
Mineral name
Topaz
Chemical formula
Al2[(F,OH)2SiO4]
Crystal system
orthorhombic
Crystal Class
orthorhombic-dipyramidal (2/m 2/m 2/m)
Space Group
Pbnm
Unit cell
a [Å]:4.65
b [Å]:8.80
c [Å]:8.40
Formula units
Z=4
Mohs hardness
8
Density [g/cm3]
3.5 - 3.6
Cleavage
perfect on (001)
Fracture / Tenacity
uneven to conchoidal
Color
yellowish brown (common), blau, violett, red, colorless
Streak
white
Transparency
transparent to translucent
Optical character
biaxial (+)
Refractive Index
nα=1.606-1.629; nβ=1.609-1.631; nΥ=1.616-1.638
Birefringence δ
0.010
Pleochroism δ
weak