a colourless or white mineral sometimes tinted by impurities, found in beds as an evaporite. It is used in the manufacture of plaster of Paris, cement, paint, school chalk, glass, and fertilizer. Composition: hydrated calcium sulphate. Formula: CaSO4.2H2O. Crystal structure: monoclinic
[C17: from Latin, from Greek gupsos chalk, plaster, cement, of Semitic origin]