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Occurs in Pinal County.

Chemical Formula: CaSO4

Specific Gravity: 2.9-3.0

Luster: Vitreous to pearly

Hardness: 3-3.5

Anhydrite is a calcium sulfate mineral that lacks water molecules in its crystal structure. It often forms in sedimentary environments, particularly evaporite deposits, and can transform between its anhydrous and hydrated forms in response to changes in temperature and humidity. Its uses in construction and industry make anhydrite economically significant.

Next Pinal County mineral: Ankerite

MinDate Anhyrite

Anhydrite is a mineral composed of calcium sulfate (CaSO4) without water molecules. It is closely related to gypsum, which is also a calcium sulfate mineral, but gypsum contains water molecules within its crystal structure. The name “anhydrite” is derived from the Greek words “an,” meaning “without,” and “hydor,” meaning “water,” reflecting its lack of water content.

The chemical formula for anhydrite is CaSO4, indicating its composition of calcium (Ca), sulfur (S), and oxygen (O). Anhydrite often forms in sedimentary environments and can be found as both sedimentary rock layers and as a mineral within other rocks.

Anhydrite can crystallize in various forms, including massive, granular, and fibrous structures. Crystals can be colorless, white, or light gray, and they often have a vitreous to pearly luster. Anhydrite’s physical properties make it distinguishable from other minerals, and it is commonly found alongside other minerals in sedimentary rocks.

One of the interesting features of anhydrite is its ability to undergo reversible changes between its anhydrous form (anhydrite) and its hydrated form (gypsum) in response to changes in temperature and humidity. This transformation is known as “dehydration” and “hydration.” Anhydrite can transform into gypsum by absorbing water vapor from the atmosphere, and gypsum can lose water to become anhydrite when heated.

Anhydrite is often associated with evaporite deposits, which form when mineral-rich solutions evaporate, leaving behind solid minerals. These deposits are common in arid or semi-arid regions and can lead to the accumulation of minerals like anhydrite, gypsum, and halite (rock salt).

Anhydrite has various industrial uses. It can be ground into a powder and used as a source of calcium sulfate in the production of plaster and wallboard. It is also used as a desiccant (drying agent) and in certain industrial processes.