The primary difference between gypsum and Plaster of Paris is that calcium sulphate dihydrate is found in the gypsum, whereas calcium sulphate hemihydrates are contained in the Plaster of Paris. A naturally occurring mineral is gypsum. This is thus the biggest distinction between plaster of paris and gypsum.
In terms of crystallisation water, Plaster of Paris is distinguished from Gypsum. Gypsum has 2 moles of crystallisation water where half a mole of crystallisation water is available as Plaster of Paris. The Plaster of Paris is made from hot gypsum.
By heating gypsum or calcium sulphate to around 140-180 degrees Celsius, the Plaster of Paris is obtained. Gypsum shapes the Paris Plaster when heated to such a temperature.