Wednesday, July 2, 2008

July 2008 Mineral of the Month: Gypsum

July 2008 Mineral of the Month


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. Crystals are tabular and diamond shaped. Rosette shaped masses are known as Desert Roses and radiating forms are termed Daisy Gypsum.

Its chemical properties are as follows:

Crystal Structure…Monoclinic
Mineral Group...Sulfates
Chemical formula...Ca(SO
4) . 2H2O
Specific Gravity...2.32
Color...Colorless, White, Gray,
Reddish, Greenish, Brownish, Yellowish

Luster...Vitreous (Pearly on cleavage)
Transparency...Transparent to Opaque