An evaporite is a sedimentary deposit of salts that have been precipitated from solution owing to the evaporation of a body of water. Evaporite deposits have the least soluble salts at the bottom (calcium salts), followed by the very soluble halite (common salt) and magnesium and potassium salts. Most important commercially are gypsum (CaSO4.2H2O), anhydrite (CaSO4), and halite (NaCl).
Alkali flats, also known as salt flats, are level, barren areas in dry regions covered with evaporites, mainly salts of the alkali metals and alkaline earth metals. Alkali flats are formed by the repeated periodic evaporation of shallow lakes lacking outlets.