Evaporites

Evaporites are chemical sedimentary rocks formed by the precipitation of minerals from evaporating brines. They develop in arid or semi-arid regions where evaporation exceeds inflow, in restricted basins such as saline bays, coastal lagoons, or continental salt lakes. As water evaporates, dissolved ions reach supersaturation and precipitate as minerals in a characteristic sequence that depends on chemistry, temperature, and salinity. Gypsum and anhydrite commonly form at moderate salinity; halite (rock salt) precipitates as salinity rises; with further concentration, potassium and magnesium salts such as sylvite, carnallite, and, in some settings, borates may be deposited.

Common evaporite minerals include halite, gypsum, anhydrite, and various potash and magnesium minerals. Deposits can appear as thick, layered beds, nodules, or crystal fans, and are often associated with coastal sabkha environments or playa lake sequences. Diagenetic processes can alter original minerals after deposition, and some evaporites may dissolve or recrystallize during burial.

Economic importance is high: evaporite deposits are major sources of rock salt and gypsum, used in food, deicing, cement, and plaster production. Potash salts provide essential fertilizers, and borates are important industrial minerals in certain basins. Beyond resource value, evaporites record past climatic and hydrologic conditions, offering critical information about the history of arid basins and their sedimentary sequences.