anhydriete

Anhydrite is a mineral with the chemical formula CaSO4 that represents the anhydrous form of calcium sulfate. It is the waterless counterpart of gypsum (CaSO4·2H2O) and shares many properties with its hydrated relative. The name derives from Greek roots meaning waterless.

Anhydrite occurs mainly in sedimentary evaporite deposits formed by the evaporation of sulfate-rich waters. It often appears in association with gypsum, halite, and other evaporite minerals. It can form by direct precipitation from saline solutions or by dehydration of gypsum during burial or heating, which removes water from the crystal structure.

In hand specimens anhydrite is typically white to gray, sometimes colorless or blue-gray, with a vitreous to pearly luster. It ranges in habit from massive to well-formed tabular or prismatic crystals. Its Mohs hardness is about 3 to 3.5, and its specific gravity is near 3.0. It has a relatively simple cleavage, and fractures are generally uneven to brittle. It is slightly soluble in water, with solubility increasing under certain conditions.

Anhydrite is an economically important industrial mineral. It serves as a source of calcium and sulfur for various chemical processes and is used in cement and plaster applications, among other uses. It also forms distinctive decorative minerals and can be a constituent of evaporite rock sequences that record ancient climatic and environmental conditions.

Etymology and synonyms: “anhydrite” comes from Greek for “waterless.” In French geology and mineralogy, the term anhédriète or anhydriète is used for the same mineral.