Natural gypsum dihydrate (CaSO4 2H2O), also known as raw gypsum, can be calcined and ground to obtain β gypsum hemihydrate (2caso4 H2O), namely building gypsum, also known as plaster and gypsum. If the calcination temperature is190 C, model gypsum can be obtained, and its fineness and whiteness are higher than those of building gypsum. If raw gypsum is calcined at 400-500℃ or above 800℃, floor gypsum can be obtained. Its setting and hardening are slow, but the strength, wear resistance and water resistance after hardening are better than ordinary building gypsum.

What is the name of white, colorless, colorless and transparent crystal? Gypsum infiltration? Sometimes it is gray, light yellow, light brown and other colors due to impurities. The stripes are white. Transparent. Glass luster, cleavage surface? Pearl luster, fiber aggregate silk luster. Cleavage is extremely complete and moderate, and the cleavage sheet splits into rhombuses with plane angles of 66 and114 respectively. Sexually fragile. The hardness is 1.5~2. Slight changes in different directions. The relative density is 2.3. Under the polarizer: colorless. Biaxial crystal (+). 2V=58 .Ng= 1.530, Nm= 1.523, Np= 1.52 1 .2V decreases with the increase of temperature, and 2V is zero around 90℃.

During the heating process, the crystal water is discharged in three stages: 105~ 180℃. First, 1 water molecule is discharged, and then half of the water molecule is immediately discharged, which is converted into calcined gypsum Ca [SO4] 0.5H2O, also known as plaster of Paris or gypsum hemihydrate. In the temperature range of 200 ~ 220℃, the remaining half of the water molecules are discharged and converted into type Ⅲ anhydrite Ca [SO4] ε H2O (0.06