Evaporites

Evaporite 1

Evaporite

Cobble encrusted with halite evaporated from theDead Sea, Israel.

Evaporite (pron.: /ɪˈvæpəraɪt/) is a name for a water-soluble mineralsediment that result from concentration and crystallization byevaporation from an aqueous solution.[1] There are two types ofevaporate deposits: marine, which can also be described as oceandeposits, and non-marine, which are found in standing bodies of watersuch as lakes. Evaporites are considered sedimentary rocks.

Formation of evaporite rocks

Although all water bodies on the surface and in aquifers containdissolved salts, the water must evaporate into the atmosphere for theminerals to precipitate. For this to happen, the water body must enter arestricted environment where water input into this environmentremains below the net rate of evaporation. This is usually an arid environment with a small basin fed by a limitedinput of water. When evaporation occurs, the remaining water is enriched in salts, and they precipitate when thewater becomes oversaturated.

Evaporite depositional environments

Marine evaporites

Anhydrite

Marine evaporites tend to have thicker deposits and are usually thefocus of more extensive research.[2] They also have a system ofevaporation. When scientists evaporate ocean water in alaboratory, the minerals are deposited in a defined order that wasfirst demonstrated by Usiglio in 1884.[2] The first phase of theexperiment begins when about 50% of the original water depthremains. At this point, minor carbonates begin to form.[2] The nextphase in the sequence comes when the experiment is left withabout 20% of its original level. At this point, the mineral gypsumbegins to form, which is then followed by halite at 10%,[2]

excluding carbonate minerals that tend not to be evaporates. Themost common minerals that are generally considered to be themost representative of marine evaporates are calcite, gypsum andanhydrite, halite, sylvite, carnallite, langbeinite, polyhalite, andkanite. Kieserite (MgSO4) may also be included, which often willmake up less than four percent of the overall content.[2] However, there are approximately 80 different minerals thathave been reported found in evaporite deposits (Stewart,1963;Warren,1999), though only about a dozen are commonenough to be considered important rock formers.[2]

Evaporite 2

Non-marine evaporitesNon-marine evaporites are usually composed of minerals that are not common in marine environments, because ingeneral the water from which non-marine evaporite precipitates have proportions of chemical elements differentfrom those found in the marine environments.[2] Common minerals that are found in these deposits include blödite,borax, epsomite, gaylussite, glauberite, mirabilite, thenardite and trona. Non-marine deposits may also contain halite,gypsum, and anhydrite, and may in some cases even be dominated by these minerals, although they did not comefrom ocean deposits. This, however, does not make non-marine deposits any less important; these deposits often helpto paint a picture into past Earth climates. Some particular deposits even show important tectonic and climaticchanges. These deposits also may contain important minerals that help in today's economy.[3] Thick non-marinedeposits that accumulate tend to form where evaporation rates will exceed the inflow rate, and where there issufficient soluble supplies. The inflow also has to occur in a closed basin, or one with restricted outflow, so that thesediment has time to pool and form in a lake or other standing body of water.[3] Primary examples of this are called"saline lake deposits".[3] Saline lakes includes things such as perennial lakes, which are lakes that are thereyear-round, playa lakes, which are lakes that appear only during certain seasons, or any other terms that are used todefine places that hold standing bodies of water intermittently or year-round. Examples of modern non-marinedepositional environments include the Great Salt Lake in Utah and the Dead Sea, which lies between Jordan andIsrael.Evaporite depositional environments that meet the above conditions include:• Graben areas and half-grabens within continental rift environments fed by limited riverine drainage, usually in

subtropical or tropical environments• Example environments at the present that match this is the Denakil Depression, Ethiopia; Death Valley,

California•• Graben environments in oceanic rift environments fed by limited oceanic input, leading to eventual isolation and

evaporation• Examples include the Red Sea, and the Dead Sea in Jordan and Israel

•• Internal drainage basins in arid to semi-arid temperate to tropical environments fed by ephemeral drainage• Example environments at the present include the Simpson Desert, Western Australia, the Great Salt Lake in

Utah•• Non-basin areas fed exclusively by groundwater seepage from artesian waters

• Example environments include the seep-mounds of the Victoria Desert, fed by the Great Artesian Basin,Australia

•• Restricted coastal plains in regressive sea environments• Examples include the sabkha deposits of Iran, Saudi Arabia, and the Red Sea; the Garabogazköl of the Caspian

Sea•• Drainage basins feeding into extremely arid environments

• Examples include the Chilean deserts, certain parts of the Sahara, and the NamibThe most significant known evaporite depositions happened during the Messinian salinity crisis in the basin of theMediterranean.

Evaporite 3

Evaporitic formations

Hopper crystal cast of halite in a Jurassic rock,Carmel Formation, southwestern Utah.

Evaporite formations need not be composed entirely of halite salt. Infact, most evaporite formations do not contain more than a few percentof evaporite minerals, the remainder being composed of the moretypical detrital clastic rocks and carbonates. Examples of evaporateformations include occurrences of evaporite sulfur in Eastern Europeand West Asia.[4]

For a formation to be recognised as evaporitic it may simply requirerecognition of halite pseudomorphs, sequences composed of someproportion of evaporite minerals, and recognition of mud cracktextures or other textures.

Economic importance of evaporites

Evaporites are important economically because of their mineralogy, their physical properties in-situ, and theirbehaviour within the subsurface.Evaporite minerals, especially nitrate minerals, are economically important in Peru and Chile. Nitrate minerals areoften mined for use in the production on fertilizer and explosives.

Thick halite deposits are expected to become an important location for the disposal of nuclear waste because of theirgeologic stability, predictable engineering and physical behaviour, and imperviousness to groundwater.Halite formations are famous for their ability to form diapirs, which produce ideal locations for trapping petroleumdeposits.

Major groups of evaporite minerals

Calcite

This is a chart that shows minerals that form the marine evaporite rocks, theyare usually the most common minerals that appear in this kind of deposit.

Evaporite 4

Mineral class Mineral name Chemical Composition

Chlorides Halite Sylvite

Carnallite

Langbeinite

Polyhalite

Kainite

NaCl KCl

KMgCl3 * 6H2O

K2Mg2(SO4)3K2Ca2Mg(SO4)6 * H2O

KMg(SO4)Cl * 3H2O

Sulfates Anhydrite Gypsum

Kieserite

CaSO4 CaSO4 * 2H2O

MgSO4 * H2O

Carbonates Dolomite Calcite

Magnesite

CaMg(CO3)2 CaCO3MgCO3

Hanksite, Na22K(SO4)9(CO3)2Cl, one of the fewminerals that is both a carbonate and a sulfate

• Halides: halite, sylvite (KCl), and fluorite• Sulfates: such as gypsum, barite, and anhydrite• Nitrates: nitratine (soda niter) and niter• Borates: typically found in arid-salt-lake deposits plentiful in the

southwestern US. A common borate is borax, which has been usedin soaps as a surfactant.

• Carbonates: such as trona, formed in inland brine lakes.• Some evaporite minerals, such as Hanksite, are from multiple

groups.

Evaporite minerals start to precipitate when their concentration inwater reaches such a level that they can no longer exist as solutes.

The minerals precipitate out of solution in the reverse order of their solubilities, such that the order of precipitationfrom sea water is1. Calcite (CaCO3) and dolomite (CaMg(CO3)2)2. Gypsum (CaSO4-2H2O) and anhydrite (CaSO4).3.3. Halite (i.e. common salt, NaCl)4. Potassium and magnesium saltsThe abundance of rocks formed by seawater precipitation is in the same order as the precipitation given above. Thus,limestone (calcite) and dolomite are more common than gypsum, which is more common than halite, which is morecommon than potassium and magnesium salts.Evaporites can also be easily recrystallized in laboratories in order to investigate the conditions and characteristics oftheir formation.

References[1][1] Jackson, Julia A., 1997, Glossary of Geology 4th edition, American Geologic Institute, Alexandria Virginia[2][2] Boggs, S., 2006, Principles of Sedimentology and Stratigraphy (4th ed.), Pearson Prentice Hall, Upper Saddle River, NJ, 662 p.[3][3] Melvin, J. L.(ed) 1991, Evaporites, petroleum and mineral resources; Elsevier, Amsterdam[4] C.Michael Hogan. 2011. Sulfur. Encyclopedia of Earth, eds. A.Jorgensen and C.J.Cleveland, National Council for Science and the

environment, Washington DC (http:/ / www. eoearth. org/ article/ Sulfur?topic=49557)

• California State University evaporites page (http:/ / seis. natsci. csulb. edu/ bperry/ Sedimentary Rocks Tour/evaporites. htm)

• Gore, Rick. "The Mediterranean: Sea of Man's Fate." National Geographic. Dec. 1982: 694-737.• Gueguen and Palciauskas (1984). Introduction to the Physics of Rocks.

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Article Sources and ContributorsEvaporite  Source: http://en.wikipedia.org/w/index.php?oldid=539689085  Contributors: 06mkittle, Anon lynx, Askewchan, Aymatth2, Blanchardb, BlueAmethyst, Bob Palin, Boleslaw,Cferrero, Christian75, DanielCD, David110994, Deflective, Drphilharmonic, Duncan.france, Dycedarg, Eztafette, Gaius Cornelius, Garranlp193, GeeJo, GeoGreg, Geolrock12, Gioto, GoodOlfactory, Greatjob, IW.HG, Iancarter, Igodard, Isaac Dupree, J.delanoy, Katoa, Kwamikagami, LAX, Looxix, MatthewDBA, Michael Hardy, Mikenorton, MountainB, Ohconfucius,Pip2andahalf, Platonicmaria, Plazak, Poolkris, Qfl247, Redvers, Rjstott, Rolinator, SchfiftyThree, Seigeftw, Siim, Stan Shebs, Szilas, Teryx, Theo Pardilla, Transcendence, Turlo Lomon,Twinsday, UnitedStatesian, Uranographer, Vidioman, Vsmith, Wilson44691, 50 anonymous edits

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