What does anhydrite mean?
Anhydrite is a naturally occurring mineral composed of anhydrous calcium sulfate, CaSO₄ — that is, calcium sulfate entirely without water in its crystal structure. It typically appears white, grey, or colourless and forms massive, granular, or fibrous masses rather than showy crystals. Geologically, it belongs to the evaporite family: it precipitates from seawater in arid basins and commonly occurs in thick beds alongside halite (rock salt) and limestone. Its closest relative is gypsum, the hydrated form of calcium sulfate, and the two readily transform into one another — anhydrite absorbs water to become gypsum near the surface, while buried gypsum can lose water to become anhydrite at depth. This hydration causes expansion, which can heave floors and damage foundations, making anhydrite a practical concern in engineering. Industrially, ground anhydrite serves in cements, plasters, floor screeds, and as a soil conditioner. The name derives from the Greek roots for 'without water', reflecting its defining chemical character.
nounA white, grey, or colourless mineral consisting of anhydrous calcium sulfate (CaSO₄), typically occurring in massive or granular form and found in evaporite deposits alongside gypsum.
- The mineral anhydrous calcium sulfate (CaSO₄), occurring in evaporite beds and used in cement, plaster, and as a drying agent.
"The core samples revealed a thick bed of anhydrite beneath the salt layer."
"Miners cut through a seam of dense white anhydrite nearly thirty metres thick."
"Because it hardens reliably when ground and mixed with water, anhydrite has long been valued as a flooring screed."
Rarely pluralised; the singular is standard even when referring to multiple occurrences or specimens.
"Thin beds of anhydrite alternate with dolomite throughout the formation."
Bury anhydrite underground and it will slowly drink water from its surroundings and swell into gypsum — enough to lift buildings and buckle roads.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of anhydrite
The word anhydrite was coined in the early nineteenth century, when mineralogists were systematically naming newly distinguished species. It combines the Greek prefix 'an-' ('not') with 'hydor' ('water'), via 'anhydros' meaning 'waterless', plus the mineralogical suffix '-ite'. The name directly encodes the mineral's chemistry: unlike its close relative gypsum, which contains water of crystallisation, anhydrite is calcium sulfate without water. The same Greek root gives rise to related terms such as 'anhydrous' and 'anhydride'.
How anhydrite is actually used
A technical term used mainly in geology, mining, and construction; rarely encountered in everyday conversation.
Easily confused with anhydrite
Gypsum is the hydrated form of calcium sulfate (CaSO₄·2H₂O), softer and less dense, whereas anhydrite is its water-free counterpart.
An anhydride is a chemical compound derived from an acid by removal of water, while anhydrite is a specific rock-forming mineral.