gypsum

n. colorless mineral from which plaster of Paris is made

Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O.
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Noun
1. a common white or colorless mineral (hydrated calcium sulphate) used to make cements and plasters (especially plaster of Paris)
(hypernym) mineral
(hyponym) alabaster
(substance-holonym) plaster of Paris, plaster
(substance-meronym) calcium, Ca, atomic number 20

(n.)
A mineral consisting of the hydrous sulphate of lime (calcium). When calcined, it forms plaster of Paris. Selenite is a transparent, crystalline variety; alabaster, a fine, white, massive variety.
  

N
gypsum; plaster figure