Natural gypsum (CaSO4 • 2H2O), also known as gypsum, could be processed into β-hemihydrate gypsum (CaSO4 • 1 / 2H2O) by calcining and grinding, namely building gypsum, plaster or stucco. If the calcination temperature is 190 ° C, we can obtain model gypsum, whose fineness and whiteness is higher than construction gypsum. If natural gypsum is calcined under 400-500 ° C or above 800 ° C temperature, the final material would be flooring gypsum, which clotting, hardening are slow, but the strength, abrasion resistance and water resistance after hardening is better, compared with ordinary building gypsum. Usually selenite is white, colorless or transparent crystal, sometimes due to impurities and ash, the appearance could be yellow, light brown and other colors.