Which one of the following is the chemical formula of gypsum?

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CaSO₄·2H₂O

Ca₂SiO₄

2CaSO₄·H₂O

CaSO₄

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This question was previously asked in

UPSC NDA-2 – 2018

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Gypsum is a mineral commonly found in evaporite deposits. Its chemical composition is calcium sulfate dihydrate, meaning it contains calcium sulfate (CaSO₄) and two molecules of water of crystallization per formula unit. The chemical formula for gypsum is CaSO₄·2H₂O.

The degree of hydration of calcium sulfate determines whether it is gypsum (dihydrate), plaster of Paris (hemihydrate), or anhydrite (anhydrous).

When gypsum (CaSO₄·2H₂O) is heated, it loses water to form calcium sulfate hemihydrate (CaSO₄·½H₂O), which is commonly known as Plaster of Paris. Further heating removes all water, resulting in anhydrous calcium sulfate (CaSO₄), or anhydrite. Gypsum is widely used in plaster, drywall (gypsum board), cement production, and as a soil conditioner.

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