Selenite (mineral)

Selenite
General
CategorySulfate mineral
Formula
(repeating unit)
CaSO4·2H2O
Crystal systemMonoclinic (2/m) Space group: A2/a
Identification
Formula mass172.17
ColorBrown green, brownish yellow, greenish, gray green, gray white
Crystal habitEarthy – dull, clay-like texture with no visible crystalline affinities, (e.g. howlite)
Cleavage[010] Perfect, [100] Distinct, [011] Distinct
FractureFibrous – thin, elongated fractures produced by crystal forms or intersecting cleavages (e.g. asbestos).
Mohs scale hardness2
LusterPearly
StreakWhite
Specific gravity2.9
Optical propertiesBiaxial (+) 2V=58
Refractive indexnα = 1.519–1.521,
nβ = 1.522–1.523,
nγ = 1.529–1.53
Birefringenceδ = 0.0090–0.0100
Other characteristicsNon-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.

  1. ^ "Gypsum Mineral Data". Weinrich Minerals, Inc. Retrieved 20 October 2013.