Sedimentary rock

Evaporites: rock salt and gypsum

Minerals precipitated from evaporating brine, where evaporation exceeds water input. From seawater, calcite begins at about 50% of the brine remaining, gypsum at about 15%, halite at about 10%, then potassium and magnesium salts such as sylvite. Gypsum loses water on burial to become anhydrite; together they often form nodular 'chicken-wire' texture. Settings include sabkhas, subsiding basins and desert playas.

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