What is the chemical name of plaster of Paris?

Plaster of Paris is a type of building material based on calcium sulphate hemihaydrate CaSO4·1/2H2O.

It is created by heating gypsum to about 150 °C. 2 CaSO4·2H2O → (2 CaSO4·H2O) + 3 H2O (released as steam).