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Gypsum

(Science: chemical) 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.

Origin: L. Gypsum, gr.; cf. Ar. Jibs plaster, mortar, Per. Jabsn lime.

Its chemical formula is CaSO4•2H2O.