An important rock-forming anhydrous mineral form of calcium sulphate, CaSO4. It is chemically similar to gypsum but is harder and heavier and crystallizes in the rhombic form (gypsum is monoclinic). Under natural conditions anhydrite slowly hydrates to form gypsum. It occurs chiefly in white and greyish granular masses and is often found in the caprock of certain salt domes. It is used as a raw material in the chemical industry and in the manufacture of cement and fertilizers.
Subjects: Earth Sciences and Geography — Chemistry.