Anhydrite, a granular, white mineral composed of calcium, sulfur, and oxygen. It is commonly found associated with gypsum. Both anhydrite and gypsum are forms of calcium sulfate, but anhydrite is harder than gypsum and, unlike gypsum, does not contain water. When exposed to water, anhydrite is slowly changed into gypsum.

Anhydrite has a number of industrial applications, including use as a drying agent and as a cement additive. Anhydrite is also used as ornamental stone and as a soil conditioner.

Anhydrite is anhydrous calcium sulfate, (CaSO4H2O).