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Definition: evaporite from Hawley's Condensed Chemical Dictionary

A mineral or rock formed by precipitation of crystals from evaporating water.


Summary Article: evaporite
From Encyclopedia of Environmental Change

A mineral, sediment or sedimentary rock that forms by chemical precipitation upon the evaporation salty water (a salt). As seawater evaporates, a sequence of evaporite minerals forms with increasing salinity. First to precipitate is calcite (CaCO3), which makes up 0.3 per cent of the total precipitates. This is followed by calcium sulfate, as anhydrite (CaSO4) and gypsum (CaSO4·2H2O), which accounts for 3.5 per cent of the precipitates; then halite or rock salt (NaCl), which makes up 78 per cent of the precipitates; and finally, a range of potassium salts, which make up the remaining 18 per cent. It has been estimated that complete evaporation of the oceans would yield an evaporite deposit with an average thickness of 60 m, but many evaporite successions in the geological record exceed 1 km in thickness and are dominated by gypsum or anhydrite: some mechanism must have operated to keep the brines concentrated to form such deposits. Models include evaporation from a shallow embayment that is continually replenished with seawater of normal salinity; repeated evaporation of a marine basin, as may have happened during the messinian salinity crisis in the Mediterranean;sabkha processes on arid coastlines; or evaporation from saline lakes (e.g. Dead Sea) or playas. Evaporite minerals also form within soils (see duricrust). Evaporite deposits in the geological record are good indicators of a palaeoenvironment that was hot and arid. Many evaporite minerals are exploited as resources with important industrial applications, and evaporite deposits commonly trap accumulations of petroleum. Evaporites in the subsurface are liable to solution by groundwater, and areas where evaporites form part of the local rock succession experience problems of ground collapse or subsidence.

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[See also seawater composition, sedimentological evidence of environmental change]

  • Hsü, KJ (1972) Origin of saline giants: A critical review after the discovery of the Mediterranean evaporite. Earth-Science Reviews 8: 371-396.
  • Kendall, CGStC; Alsharhan, AS (eds) (2010) Quaternary carbonate and evaporate sedimentary facies and their ancient analogues. Chichester: Wiley-Blackwell.
  • Schreiber, BC, Lugli, S; Babel, M (eds) (2007) Evaporites through space and time. Bath: Geological Society.
  • Warren, JK (2006) Evaporites: Sediments, resources and hydrocarbons. Berlin: Springer.
Andrew D. Thomas
University of Salford
© by SAGE Publications Ltd.

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