Gypsum

A widespread calcium sulphate hydrate of economic importance, Gypsum occurs as a mineral or a rock. When formed as a rock it is also known as Gyprock. About 75% of gypsum that is mined, is heat treated for use as plaster of Paris. Unaltered rock gypsum is used as fertilizer, a fluxing agent, filler in paper and textiles and retardant in Portland cement. As a mineral it can be white, or colourless or tinted yellow, green, brown, grey or orange due to impurities. Satin spar is a form of gypsum crystal that can be cut into a gem that has a cat's eye shine.