EVAPORITE

any of a variety of individual minerals found in the sedimentary deposit of soluble salts that results from the evaporation of water. Typically, evaporite deposits occur in closed marine basins where evaporation exceeds inflow. The deposits often show a repeated sequence of minerals, indicating cyclic conditions with a mineralogy determined by solubility. The most important minerals and the sequence in which they form include calcite, gypsum, anhydrite, halite, polyhalite, and lastly potassium and magnesium salts such as sylvite, carnallite, kainite, and kieserite; anhydrite and halite dominate. These sequences have been reproduced in laboratory experiments and, therefore, the physical and chemical conditions for evaporite formation are well known. In contrast to basin deposits, extensive thin-shelf deposits are known and are thought to be the result of shallow, ephemeral seas. Non-marine evaporites formed by streams flowing into closed depressions, especially in arid regions, give rise to deposits of borates, nitrates, and sodium carbonates. Such deposits occur in Utah and southern California in the United States.