Gypsum is a common mineral, with thick and extensive evaporised beds in association with sedimentary rocks . Deposits are known to occur in strata from as early as the Permian age. . Hydrothermal anhydrite in veins is commonly hydrated to gypsum by groundwater in near surface exposures. It is often associated with the minerals halite and sulfur.
The raw material gypsum is sorted and washed with water for removal of sand and other impurities. The lumps thus obtained are then dried and powdered in pulverizer. The dried gypsum powder is calcined in a rotary drumcalciner using light diesel oil as fuel. The low pressure burner is used for calcination at a temperature of 160ºC to 180ºC. The process of calcination is done over a period of about 2 hours, so that one and half molecules of water is removed to convert the gypsum (CaSo4 2 H2O) into plaster of paris (CaSo4 ½ H2O). After cooling the product (plaster of paris) is further pulverised to a fineness of 150 mesh and packed in air tight polythene lined gunny bags to avoid the plaster of paris from absorption of moisture. For manufacture of surgical grade plaster of paris, a mineral silinite which is considered to be a purer variety of gypsum is used.