Gypsum is a soft sulfate mineral composed of calcium sulfate dehydrate, with the chemical formula CaSO4·2H2O. It is widely mined and is used as a fertilizer, and as the main constituent in many forms of plaster, blackboard chalk and wallboard. A massive fine-grained white or lightly tinted variety of gypsum, called alabaster, has been used for sculpture by many cultures including Ancient Egypt, Mesopotamia, Ancient Rome, Byzantine empire and the Nottingham alabaster of medieval England. It is the definition of a hardness of 2 on the Mohs scale of mineral hardness. It forms as an evaporate mineral and as a hydration product of anhydrous.