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:
Chemical formula...Ca(SO4) . 2H2O
Color...Colorless, White, Gray, Reddish, Greenish, Brownish, Yellowish
Luster...Vitreous (Pearly on cleavage)
Transparency...Transparent to Opaque