Mineral - Gypsum
Gypsum
Chemical Properties
Mineral Class
Sulphates
Toxicity
none
Formula
Ca[SO₄]·2H₂O
Unit Cell
a=5.68 b=15.20 c=6.52 β=118° Z=4
Physical Properties
Hardness
2
Streak
white
Density
Normal (2-3,5)
Cleavage
Perfect after {010}, distinct after {100}
Fracture
conchoidal,
splintery
Tenacity
Inelastic-flexible
Optical Properties
Color
whitebrowngrayredgreencolorless
Birefringence
0.010
Luster
Vitreous,
Silky,
Pearly
Transparency
translucent,
transparent,
opaque
Pleochroism
Geomineralogical Properties
Crystal System
monoclinic
Point Group
monoclinic-prismatic - 2/m
Space Group
C2/c (15)
Habit
coarse, crusty, lenticular, curly, massive, acicular, prismatic, Rhombohedron, spear-shaped, stalactitic, star-shaped, tabular
Formation
(1) As an evaporite, by direct precipitation from seawater when the solubility product is exceeded, through evaporation in arid climates.
(2) Secondary, through the hydration of dry calcium sulfate (Anhydrite)
(3) Secondary, through aqueous oxidation of sulfides (often Pyrite) in a carbonatic environment
Paragenesis
Twinning
Swallowtail-shaped, spear-shaped, or butterfly-shaped contact or interpenetrating twins after {100}, {10 1 }, {001}, { 2 01}, or {101}
Rarity
Very common
Synonyms
Gypsum, Alabaster, Selenit, Desert Rose, Sand Rose, Gypsum rose
Composition
Elements
Mass
SO₃
46.00
CO₂
0.28
CaO
32.36
H₂O
20.28
Ukraine (Palache et al. 1952)
Groups and Members
Gypsum-Supergroup