What is an evaporite in geology ?

Evaporite : definition

Evaporites are sedimentary rocks rich in chlorides and alkaline sulphates, originating from the precipitation of salts contained in sea water (in the case of lagoons) or in salt lakes, following intense evaporation.

The essential minerals of marine evaporites are gypsum, anhydrite, halite and sylvite, but the accessory minerals are numerous. Evaporites play an important geological role since they constitute thick sedimentary levels (sometimes several thousand meters), which often play the role of a soap layer (fragile and deformable level on which large rocky planes can slide).

Their economic role is essential since rock salt, plaster (by calcination of gypsum) and potash (a mixture of halite and sylvite) are drawn from them. Under the weight of the rocks, the evaporites buried at great depth can rise by gravity, constituting the salt domes (or salt diapirs): this is the phenomenon of halokinesis.

Continental evaporites are less important geologically. They form in closed desert areas, often by evaporation of brines of volcanic origin. Their mineralogy is different and mainly comprises borates and nitrates.