The Probert Encyclopaedia of Rocks & Minerals

GYPSUM

Gypsum is a common mineral distributed in sedimentary rocks, often as thick beds. Gypsum is usually found under beds of rock salt as it's one of the first minerals to crystallize from evaporated salt waters and is also produced in volcanic areas and in rock veins due to the action of sulphuric acid. Gypsum is used in the production of plaster of Paris. It has the formulae CaSO4.2H2O and a relative hardness of 2.
Research Gypsum