Calcination: The Powdered gypsum is heated to get rid of h2o molecules, generating diverse varieties of plaster depending upon the temperature and length of heating. Map of gypsum deposits in northern Ohio, black squares reveal The placement of deposits, from "Geography of Ohio", 1923 Gypsum is used in numerous types https://www.propanraya.com/id/produk/eco-gypsum-ee-4050