Anhydrite

Anhydrite is a calcium sulfate mineral with the formula CaSO₄. It commonly forms in evaporite deposits and can hydrate to gypsum when exposed to water.

Calcium sulfate: An inorganic compound composed of calcium, sulfur, and oxygen, occurring in several hydration states. Anhydrite is the water-free mineral form of this compound.
Evaporite: A sedimentary deposit formed when dissolved minerals precipitate as water evaporates. Anhydrite commonly precipitates in the evaporite sequences where it is found.
Anhydrite screed: A calcium sulfate-based floor screed, commonly made with anhydrite binder. Its binder derives from anhydrite and sets into a smooth flooring layer.
Bassanitе: A calcium sulfate mineral with the formula CaSO₄·0.5H₂O, intermediate in hydration between anhydrite and gypsum. Its partial hydration makes it a distinct intermediate rather than water-free anhydrite.
Sulfate mineral: A mineral containing the sulfate anion, SO₄²⁻, as a major structural component. Anhydrite belongs to this mineral class through its sulfate groups.
Evaporite sequence: A layered succession of salts deposited as a body of saline water becomes concentrated. Anhydrite's position among evaporite layers reflects changing water chemistry and concentration.
Plaster: A workable paste that hardens into a solid coating, often made from gypsum or related materials. Processed anhydrite can serve as a binder in plaster and other building products.
Barite: A barium sulfate mineral, BaSO₄, known for its high density. Barite resembles anhydrite in being a sulfate mineral but contains barium instead of calcium.
Crystal system: A classification of crystals by their symmetry and lattice geometry. Anhydrite crystallizes in the orthorhombic system, unlike gypsum's monoclinic structure.
Gypsum–anhydrite transition: The temperature- and pressure-dependent conversion between gypsum and anhydrite through water loss or uptake. This transition controls whether calcium sulfate occurs as anhydrite or hydrated gypsum.

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