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 |
Molecular weight [g/mol]
182.25 |
Formula units
Z=4 |
Twinning
Rarely on [111] |
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 |
Luster
vitreous |
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 |