Gypsum plaster of paris Gypsum is a naturally occurring soft-sulfate mineral deposited from lake and sea water and found in layers of sedimentary rocks. On the other hand, Gypsum Plaster of Paris is produced by heating gypsum or calcium sulphate to a very high temperature of 120 degree celsius for an hour. Gypsum (CaSO4.2H2O) has 2 moles of crystallized water and three quarters of this water evaporates on careful heating to form plaster of paris (CaSO4.1/2 H2O) with half mole of crystallized water. Gypsum on heating turns into a white powder which is what we call Plaster of Paris, and on mixing this with water it turns into a gypsum paste which is used in false ceilings, wall surfaces, as fireproof agents, etc. Plaster of Paris is named so because it is prepared from heating the gypsum that is found abundantly in Montmartre hill near Paris. https://kanishplasters.com/is-the-plaster-of-paris-and-gypsum-plaster-the-same/