Gypsum and Plaster of Paris

 Gypsum and Plaster of Paris are not the same, although they are related. Gypsum is a naturally occurring soft sulfate mineral deposited from lake and sea water and found in layers of sedimentary rocks. It has calcium sulphate dihydrate (CaSO4.2H2O). Plaster of Paris, on the other hand, is produced by heating gypsum or calcium sulphate to a very high temperature of 120 degrees Celsius for an hour. Plaster of Paris is a building material that is used for protective or decorative purposes. It is a quick-setting gypsum plaster consisting of a fine white powder (calcium sulfate hemihydrate), which hardens when moistened and allowed to dry. Plaster of Paris is commonly used to precast and hold parts of ornamental plasterwork placed on ceilings and cornices, and in medicine to make plaster casts to immobilize broken bones while they heal.