(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}, {101}, {001}, {201}, or {101}
Rarity
Very common
Synonyms
Gypsum, Alabaster, Selenit, Desert Rose, Sand Rose, Gypsum rose
