Gypsum is a soft sulfate mineral composed of calcium sulfate dehydrate, with the chemical formula CaSO. 4· 2H2O Gypsum is widely used in construction because of its ability to hold nails, screws and other small parts. Some gypsum products are used to make drywall, plaster foundation and facing materials, concrete and stucco. Chemical Specifications: CaSO. 4· 2H2O 95-98%