Selenite | |
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General | |
Category | Sulfate mineral |
Formula (repeating unit) | CaSO4·2H2O |
Crystal system | Monoclinic (2/m) Space group: A2/a |
Identification | |
Formula mass | 172.17 |
Color | Brown green, brownish yellow, greenish, gray green, gray white |
Crystal habit | Earthy – dull, clay-like texture with no visible crystalline affinities, (e.g. howlite) |
Cleavage | [010] Perfect, [100] Distinct, [011] Distinct |
Fracture | Fibrous – thin, elongated fractures produced by crystal forms or intersecting cleavages (e.g. asbestos). |
Mohs scale hardness | 2 |
Luster | Pearly |
Streak | White |
Specific gravity | 2.9 |
Optical properties | Biaxial (+) 2V=58 |
Refractive index | nα = 1.519–1.521, nβ = 1.522–1.523, nγ = 1.529–1.53 |
Birefringence | δ = 0.0090–0.0100 |
Other characteristics | Non-radioactive, non-magnetic, fluorescent |
References | [1] |
Selenite, satin spar, desert rose, and gypsum flower are crystal habit varieties of the mineral gypsum.
All varieties of gypsum, including selenite and alabaster, are composed of calcium sulfate dihydrate (meaning that it has two molecules of water), with the chemical formula CaSO4·2H2O. Selenite contains no significant selenium – The similar names both derive from Greek selḗnē (σελήνη 'Moon').
Some of the largest crystals ever found are of selenite, the largest specimen found in the Naica Mine's Cave of the Crystals being 12 metres long and weighing 55 tons.