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An evaporite () is a water- soluble
sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
deposit that results from concentration and
crystallization Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposi ...
by
evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when h ...
from an
aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be r ...
. There are two types of evaporite deposits: marine, which can also be described as ocean deposits, and non-marine, which are found in standing bodies of water such as lakes. Evaporites are considered
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
s and are formed by chemical
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...
s.


Formation of evaporite rocks

Although all water bodies on the surface and in aquifers contain dissolved salts, the water must evaporate into the atmosphere for the minerals to precipitate. For this to happen, the water body must enter a restricted environment where water input into this environment remains below the net rate of evaporation. This is usually an
arid A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ...
environment with a small basin fed by a limited input of water. When evaporation occurs, the remaining water is enriched in salts, and they precipitate when the water becomes supersaturated.


Evaporite depositional environments


Marine evaporites

Marine evaporites tend to have thicker deposits and are usually the focus of more extensive research. When scientists evaporate ocean water in a laboratory, the minerals are deposited in a defined order that was first demonstrated by Usiglio in 1884. The first phase of precipitation begins when about 50% of the original water depth remains. At this point, minor
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
s begin to form. The next phase in the sequence comes when the experiment is left with about 20% of its original level. At this point, the mineral
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywa ...
begins to form, which is then followed by
halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...
at 10%, excluding carbonate minerals that tend not to be evaporites. The most common marine evaporites are
calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...
,
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywa ...
and anhydrite,
halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...
,
sylvite Sylvite, or sylvine, is potassium chloride (KCl) in natural mineral form. It forms crystals in the isometric system very similar to normal rock salt, halite ( NaCl). The two are, in fact, isomorphous. Sylvite is colorless to white with shades o ...
,
carnallite Carnallite (also carnalite) is an evaporite mineral, a hydrated potassium magnesium chloride with formula KMgCl3·6(H2O). It is variably colored yellow to white, reddish, and sometimes colorless or blue. It is usually massive to fibrous with rar ...
, langbeinite, polyhalite, and
kainite Kainite ( or ) (KMg(SO4)Cl·3H2O) is an evaporite mineral in the class of "Sulfates (selenates, etc.) with additional anions, with H2O" according to the Nickel–Strunz classification. It is a hydrated potassium-magnesium sulfate-chloride, natura ...
. Kieserite (MgSO4) may also be included, which often will make up less than four percent of the overall content. However, there are approximately 80 different minerals that have been reported found in evaporite deposits, though only about a dozen are common enough to be considered important rock formers.


Non-marine evaporites

Non-marine evaporites are usually composed of minerals that are not common in marine environments because in general the water from which non-marine evaporite precipitates has proportions of chemical elements different from those found in the marine environments. Common minerals that are found in these deposits include blödite,
borax Borax is a salt (ionic compound), a hydrated borate of sodium, with chemical formula often written . It is a colorless crystalline solid, that dissolves in water to make a basic solution. It is commonly available in powder or granular form ...
, epsomite, gaylussite, glauberite, mirabilite, thenardite and
trona Trona (trisodium hydrogendicarbonate dihydrate, also sodium sesquicarbonate dihydrate, Na2CO3•2NaHCO3•3H2O) is a non- marine evaporite mineral. It is mined as the primary source of sodium carbonate in the United States, where it has repla ...
. 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 come from ocean deposits. This, however, does not make non-marine deposits any less important; these deposits often help to paint a picture into past Earth climates. Some particular deposits even show important tectonic and climatic changes. These deposits also may contain important minerals that help in today's economy. Thick non-marine deposits that accumulate tend to form where evaporation rates will exceed the inflow rate, and where there is sufficient soluble supplies. The inflow also has to occur in a closed basin, or one with restricted outflow, so that the sediment has time to pool and form in a lake or other standing body of water. Primary examples of this are called "saline lake deposits". Saline lakes includes things such as perennial lakes, which are lakes that are there year-round, playa lakes, which are lakes that appear only during certain seasons, or any other terms that are used to define places that hold standing bodies of water intermittently or year-round. Examples of modern non-marine depositional environments include the
Great Salt Lake The Great Salt Lake is the largest saltwater lake in the Western Hemisphere and the eighth-largest terminal lake in the world. It lies in the northern part of the U.S. state of Utah and has a substantial impact upon the local climate, particu ...
in Utah and the
Dead Sea The Dead Sea ( he, יַם הַמֶּלַח, ''Yam hamMelaḥ''; ar, اَلْبَحْرُ الْمَيْتُ, ''Āl-Baḥrū l-Maytū''), also known by other names, is a salt lake bordered by Jordan to the east and Israel and the West Ban ...
, which lies between Jordan and Israel. Evaporite
depositional environments In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will b ...
that meet the above conditions include: *
Graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic conte ...
areas and
half-graben A half-graben is a geological structure bounded by a fault along one side of its boundaries, unlike a full graben where a depressed block of land is bordered by parallel faults. Rift and fault structure A rift is a region where the lithosphere ...
s 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 Death Valley is a desert valley in Eastern California, in the northern Mojave Desert, bordering the Great Basin Desert. During summer, it is the hottest place on Earth. Death Valley's Badwater Basin is the point of lowest elevation in Nort ...
,
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
* 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 The Dead Sea ( he, יַם הַמֶּלַח, ''Yam hamMelaḥ''; ar, اَلْبَحْرُ الْمَيْتُ, ''Āl-Baḥrū l-Maytū''), also known by other names, is a salt lake bordered by Jordan to the east and Israel and the West Ban ...
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 Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to t ...
, the
Great Salt Lake The Great Salt Lake is the largest saltwater lake in the Western Hemisphere and the eighth-largest terminal lake in the world. It lies in the northern part of the U.S. state of Utah and has a substantial impact upon the local climate, particu ...
in
Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...
* 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 The Great Artesian Basin (GAB), located in Australia, is the largest and deepest artesian basin in the world, stretching over , with measured water temperatures ranging from . The basin provides the only source of fresh water through much of ...
, Australia * Restricted coastal plains in regressive sea environments ** Examples include the sabkha deposits of Iran, Saudi Arabia, and the Red Sea; the
Garabogazköl The Garabogazköl (also spelt Kara-Bogaz-Gol; "Black Strait Lake"), or Garabogazköl Aylagy ("Black Strait Lake Bay"), is a shallow, highly-saline water-filled depression in the northwestern corner of Turkmenistan. It forms a lagoon of the Caspian ...
of the
Caspian Sea The Caspian Sea is the world's largest inland body of water, often described as the world's largest lake or a full-fledged sea. An endorheic basin, it lies between Europe and Asia; east of the Caucasus, west of the broad steppe of Central A ...
* Drainage basins feeding into extremely arid environments ** Examples include the Chilean deserts, certain parts of the
Sahara , photo = Sahara real color.jpg , photo_caption = The Sahara taken by Apollo 17 astronauts, 1972 , map = , map_image = , location = , country = , country1 = , ...
, and the Namib The most significant known evaporite depositions happened during the Messinian salinity crisis in the basin of the
Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on ...
.


Evaporitic formations

Evaporite formations need not be composed entirely of
halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...
salt. In fact, most evaporite formations do not contain more than a few percent of evaporite minerals, the remainder being composed of the more typical detrital
clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...
rocks and
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
s. Examples of evaporite formations include occurrences of evaporite sulfur in Eastern Europe and West Asia. For a formation to be recognised as evaporitic it may simply require recognition of halite
pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form ( crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced ...
s, sequences composed of some proportion of evaporite minerals, and recognition of mud crack textures or other textures.


Economic importance

Evaporites are important economically because of their mineralogy, their physical properties in-situ, and their behaviour within the subsurface. Evaporite minerals, especially nitrate minerals, are economically important in Peru and Chile. Nitrate minerals are often mined for use in the production on
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
and
explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...
s. Thick halite deposits are expected to become an important location for the disposal of nuclear waste because of their geologic stability, predictable engineering and physical behaviour, and imperviousness to groundwater. Halite formations are famous for their ability to form
diapir A diapir (; , ) is a type of igneous intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–T ...
s, which produce ideal locations for trapping
petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
deposits. Halite deposits are often mined for use as
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
.


Major groups of evaporite minerals

This is a chart that shows minerals that form the marine evaporite rocks, they are usually the most common minerals that appear in this kind of deposit. : * Halides:
halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...
,
sylvite Sylvite, or sylvine, is potassium chloride (KCl) in natural mineral form. It forms crystals in the isometric system very similar to normal rock salt, halite ( NaCl). The two are, in fact, isomorphous. Sylvite is colorless to white with shades o ...
(KCl), and fluorite * Sulfates: such as
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywa ...
,
barite Baryte, barite or barytes ( or ) is a mineral consisting of barium sulfate ( Ba S O4). Baryte is generally white or colorless, and is the main source of the element barium. The ''baryte group'' consists of baryte, celestine (strontium sulfate), ...
, and anhydrite *
Nitrates Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...
:
nitratine Nitratine or nitratite, also known as cubic niter (UK: nitre), soda niter or Chile saltpeter (UK: Chile saltpetre), is a mineral, the naturally occurring form of sodium nitrate, NaNO3. Chemically it is the sodium analogue of saltpeter. Nitratine ...
(soda niter) and niter * Borates: typically found in arid-salt-lake deposits plentiful in the southwestern US. A common borate is
borax Borax is a salt (ionic compound), a hydrated borate of sodium, with chemical formula often written . It is a colorless crystalline solid, that dissolves in water to make a basic solution. It is commonly available in powder or granular form ...
, which has been used in
soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are us ...
s as a
surfactant Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsion#Emulsifiers , ...
. * Carbonates: such as
trona Trona (trisodium hydrogendicarbonate dihydrate, also sodium sesquicarbonate dihydrate, Na2CO3•2NaHCO3•3H2O) is a non- marine evaporite mineral. It is mined as the primary source of sodium carbonate in the United States, where it has repla ...
, formed in inland brine lakes. ** Some evaporite minerals, such as Hanksite, are from multiple groups. Evaporite minerals start to precipitate when their concentration in water reaches such a level that they can no longer exist as
solutes In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solven ...
. The minerals precipitate out of solution in the reverse order of their solubilities, such that the order of precipitation from sea water is: #
Calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...
(CaCO3) and
dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...
() # Gypsum () and anhydrite (CaSO4). # Halite (i.e. common salt, NaCl) #
Potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...
and
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
salts The abundance of rocks formed by seawater precipitation is in the same order as the precipitation given above. Thus,
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...
(
calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...
) and
dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...
are more common than
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywa ...
, which is more common than
halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...
, which is more common than
potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...
and
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
salts. Evaporites can also be easily recrystallized in laboratories in order to investigate the conditions and characteristics of their formation.


Possible evaporites on Titan

Recent evidence from satellite observations and laboratory experiments suggest evaporites are likely present on the surface of
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...
, Saturn's largest moon. Instead of water oceans, Titan hosts lakes and seas of liquid hydrocarbons (mainly methane) with many soluble hydrocarbons, such as
acetylene Acetylene ( systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...
, that can evaporate out of solution. Evaporite deposits cover large regions of Titan's surface, mainly along the coastlines of lakes or in isolated
basins Basin may refer to: Geography and geology * Depression (geology) ** Back-arc basin, a submarine feature associated with island arcs and subduction zones ** Debris basin, designed to prevent damage from debris flow ** Drainage basin (hydrology), a ...
( Lacunae) that are equivalent to salt pans on Earth.


See also

*
List of minerals This is a list of minerals for which there are articles on Wikipedia. Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various ''species''. Within a m ...
*
List of rock types The following is a list of rock types recognized by geologists. There is no agreed number of specific types of rocks. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can des ...
*
Salt dome A salt dome is a type of structural dome formed when salt (or other evaporite minerals) intrudes into overlying rocks in a process known as diapirism. Salt domes can have unique surface and subsurface structures, and they can be discovered usi ...


References


Other reading


California State University evaporites page
* * * Hardie, Lawrence, 1984, Evaporites: marine or nonmarine?: American Journal of Science, v. 284, pp. 193-240. DOI: https://doi.org/10.2475/ajs.284.3.193 * Hardie, L.A., and Eugster, H.P., 1971, The depositional environment of marine evaporites: a case for shallow, clastic accumulation: Sedimentology, v. 16, p. 187–220. * Benison, K.C., and Goldstein, R.H., 2002, Recognizing acid lakes and groundwaters in the rock record: Sedimentary Geology, v. 151, p. 177-185. {{Authority control Sedimentary rocks Mineralogy