Aluminium Hydroxy Fluoro Silicate
Al2[(F,OH)2SiO4]
![Aluminium Hydroxy Fluoro Silicate - Al2[(F,OH)2SiO4]](../bilder/kristalle/Topaz-2442.jpg "Aluminium Hydroxy Fluoro Silicate - Al2[(F,OH)2SiO4]")
![Aluminium Hydroxy Fluoro Silicate - Al2[(F,OH)2SiO4]](../bilder/kristalle/Topaz-2448.jpg "Aluminium Hydroxy Fluoro Silicate - Al2[(F,OH)2SiO4]")
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Chemical name
Aluminium Hydroxy Fluoro Silicate |
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Mineral name
Topaz |
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Chemical formula
Al2[(F,OH)2SiO4] |
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Crystal system
orthorhombic |
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Crystal Class
orthorhombic-dipyramidal (2/m 2/m 2/m) |
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Space Group
Pbnm |
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Unit cell
a [Å]:4.65 b [Å]:8.80 c [Å]:8.40 |
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Molecular weight [g/mol]
182.25 |
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Formula units
Z=4 |
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Twinning
Rarely on [111] |
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Mohs hardness
8 |
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Density [g/cm3]
3.5 - 3.6 |
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Cleavage
perfect on (001) |
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Fracture / Tenacity
uneven to conchoidal |
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Color
yellowish brown (common), blau, violett, red, colorless |
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Streak
white |
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Transparency
transparent to translucent |
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Luster
vitreous |
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Optical character
biaxial (+) |
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Refractive Index
nα=1.606-1.629; nβ=1.609-1.631; nΥ=1.616-1.638 |
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Birefringence δ
0.010 |
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Pleochroism δ
weak |
