Calcium sulphate (or calcium sulfate) is a common laboratory and industrial chemical. In the form of gamma-anhydrite (the nearly anhydrous form), it is used as a desiccant. It is also used as a coagulant in products like tofu. In the natural state, unrefined calcium sulphate is a translucent, crystalline white rock. When sold as a colour-indicating variant under the name Drierite, it appears blue or pink due to impregnation with Cobalt(II) chloride, which functions as a moisture indicator. The hemihydrate (CaSO4.~0.5H2O) is better known as plaster of Paris, while the dihydrate (CaSO4.2H2O) occurs naturally as gypsum. The anhydrous form occurs naturally as beta-anhydrite. Depending on the method of calcination of calcium sulphate dihydrate, specific hemihydrates are sometimes distinguished: alpha-hemihydrate and beta-hemihydrate. They appear to differ only in crystal shape. Alpha-hemihydrate crystals are more prismatic than beta-hemihydrate crystals and, when mixed with water, form a much stronger and harder superstructure.

Used as a common component of fouling deposits in industrial heat exchanges

Minimum Assay: <96%
Molecular Formula: CaO4S
Molecular Weight: 136.14
Solubility in water: 0.24g in 100g water
Melting Point: 1450°C
Density (g/cm3): 2.96
Loss on ignition: <2.85%

Hazard Phrases: Not considered harmful under normal laboratory conditions

Cas No: 7778-18-9
Einecs No: 231-900-3