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

Gypsum is a naturally occurring mineral chemically identified as hydrous calcium sulphate [4]. Its chemical formula is CaSO4·2H2O, which signifies that it is a dihydrate containing two molecules of water of crystallisation for every unit of calcium sulphate [5]. When gypsum is heated to approximately 373 K, it loses part of its water content to become Plaster of Paris (calcium sulphate hemihydrate, CaSO4·1/2H2O) [1]. Conversely, when Plaster of Paris is mixed with water, it rehydrates to form a hard solid mass of gypsum [1]. Gypsum is widely used in the cement industry to regulate setting time, as well as in the production of fertilisers and ceramics [4]. Other forms of calcium sulphate include anhydrite (CaSO4), which lacks water of crystallisation [5].

Sources

1. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > 13.5. Some Rock-Forming Minerals > p. 175
2. [4] https://pubchem.ncbi.nlm.nih.gov/compound/Calcium-Sulfate-Dihydrate
3. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Plaster of Paris > p. 33
4. [5] https://core.ac.uk/download/pdf/185697003.pdf