Gypsum
Named in antiquity from the Greek word "gypsos," meaning plaster. It can be found as a massive material including the Alabaster variety and also as clear crystals in the Selenite variety. It can also form as a parallel fibrous growth known as the Satin Spar variety. Commonest of the sulphate minerals, gypsum is found in marine evaporates, in caves where the air is dry enough to allow it to be deposited and remain, at fumaroles, and, on occasion, in the oxidized zones of sulfide deposits.
Its chemical properties are as follows:
Crystal Structure…Monoclinic
Mineral Group...Sulfates
Chemical formula...Ca(SO4) . 2H2O
Specific Gravity...2.32
Tenacity…Brittle
Color...Colorless, White, Gray, Reddish, Greenish, Brownish, Yellowish
Hardness...2
Luster...Vitreous (Pearly on cleavage)
Transparency...Transparent to Opaque
Streak...White
Cleavage...Perfect
Fracture...Splintery
