CaSO4.2H2Ogypsum→'T'kelvin2CaSO4.H2OPlaster of paris. ‘T’ is about

When gypsum is heated at about 393 K it gets converted to plaster of Paris.If the temperature becomes greater than 393 K, gypsum loses all the water of crystallization, setting property is lost. Anhydrous CaSO4 so formed is called “Dead burnt plaster” (or) “Dead burnt gypsum”.