Gypsum

Gypsum is hydrous calcium sulphate crystallising in the monoclinic system. Crystals are common. Twin crystals are also common. Its hardness is 2 and the specific gravity is 2.3. Its lustre is either pearly, vitreous, silky or earthy. It is colourless or white, grey, pink, brown or black in colour. It produces a white streak. The mineral dissolves readily in hydrochloric acid. Gypsum is used in the manufacture of cement and plaster of Paris. In agriculture it is used as a fertiliser. In Tamilnadu, gypsum occurs in Tiruchirapalli, Tirunelveli, Coimbatore and Chingelput districts of Tamilnadu.