Gypsum

Gypsum is a soft mineral composed of calcium sulfate dihydrate, CaSO₄·2H₂O. It commonly forms by evaporation of saline water and is the raw material for plaster and drywall.

Calcium sulfate: An inorganic compound with formula CaSO₄, occurring in anhydrous and hydrated forms. Gypsum is the dihydrate form of this compound.
Evaporite: A sedimentary rock formed when dissolved minerals precipitate as water evaporates. Gypsum is a common mineral in evaporite deposits.
Plaster of Paris: A powder of partially dehydrated gypsum that hardens when mixed with water. Heating gypsum creates this material, which sets as it rehydrates.
Naica Mine: A mine in Chihuahua, Mexico, famous for exceptionally large gypsum crystals in the Cave of the Crystals. Its giant selenite crystals grew in a warm, mineral-rich cave.
Crystal structure: The ordered three-dimensional arrangement of atoms or ions in a crystalline solid. Gypsum’s layered structure helps explain its softness and cleavage.
Evaporite sequence: A recurring order of minerals deposited as a body of saline water becomes progressively concentrated by evaporation. Gypsum precipitates at an intermediate stage of seawater evaporation.
Drywall: A building panel made from a gypsum core faced with paper or other coverings. Gypsum’s fire resistance and availability make it the panel’s main core material.
Cave of the Crystals: A cavern at Naica, Mexico, containing some of the largest natural gypsum crystals ever documented. The cave is a spectacular example of gypsum crystal growth.
Mohs scale: A scale that ranks minerals by their resistance to scratching, from talc to diamond. Gypsum’s hardness of 2 makes it scratchable by a fingernail.
Anhydrite: An anhydrous calcium sulfate mineral with formula CaSO₄. It lacks gypsum’s water molecules and can form through gypsum dehydration.

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