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.
Nodular anhydrite (Arab Formation)Gypsum(dark lenticular shapes) in brown/grey lime mudstone (lens 2.5cm sq) What environment do these structures/textures occur in?
The normal sulphates are the more important, and occur widely and abundantly distributed in the mineral kingdom; anhydrite, gypsum, anglesite, barytes, celestite and kieserite are among the commonest species.
The salt is commonly associated with gypsum, often also with anhydrite, and occasionally with sylvite, carnallite and other minerals containing potassium and magnesium.
Thus the sulphate constitutes the minerals anhydrite, alabaster, gypsum, and selenite; the carbonate occurs dissolved in most natural waters and as the minerals chalk, marble, calcite, aragonite; also in the double carbonates such as dolomite, bromlite, barytocalcite; the fluoride as fluorspar; the fluophosphate constitutes the mineral apatite; while all the more important mineral silicates contain a proportion of this element.