When gypsum rock is crushed and the water removed, it can be used to make plaster of paris, commonly used in industry. Ground gypsum is also used as a soil conditioner. Chemically, gypsum rock is calcium sulfate with two molecules of water.
Gypsum rock is mined or quarried, crushed and ground into a fine powder. In a process called calcining, the powder is heating to approximately 350 degrees F, driving off three fourths of the chemically combined water.