Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO₄·2H₂O. It can be used as a fertilizer, is the main constituent in many forms of plaster and is widely mined. A very fine-grained white or lightly tinted variety of gypsum, called alabaster, has been used for sculpture by many cultures including Ancient Egypt, Mesopotamia and the Nottingham alabasters of medieval England. It is the definition of a hardness of 2 on the Mohs scale of mineral hardness. It forms as an evaporite mineral and as a hydration product of anhydrite.