Rock-forming mineral, anhydrous calcium sulfate (CaSO), which differs chemically from gypsum (to which it changes in humid conditions) by having no water of crystallization. Anhydrite occurs most often with salt deposits in association with gypsum, as in the cap rock of the Texas-Louisiana salt domes. Anhydrite is one of the major minerals in evaporite deposits; it is also present in dolomites and limestones, and in ore veins. It is used in plasters and cement as a drying agent.
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