Calcium sulphate, CaSO 4, constitutes the minerals anhydrite (q.v.), and, in the hydrated form, selenite, gypsum (q.v.), alabaster (q.v.), and also the adhesive plaster of Paris (see Cement).
Deeper down there are successively strata of polyhalite, MgS04 K2S04.2CaS04.2H20, and anhydrite, CaSO 4, interspersed with regular layers of rock-salt; whilst below the anhydrite we have the main rock-salt deposits.