Editing Peridotite (section)

==Distribution and location==
[[File:Iddingsite.JPG|thumb|[[Olivine]] in a peridotite [[weathering]] to [[iddingsite]] within a [[Mantle (geology)|mantle]] [[xenolith]]]]
[[File:Serpentinized and carbonated peridotite.jpg|thumb|Serpentinized and carbonated peridotite<ref name=DCOdecadal>{{cite book |last1=Deep Carbon Observatory |title=Deep Carbon Observatory: A Decade of Discovery |doi=10.17863/CAM.44064 |date=2019 |location=Washington, DC |url=https://deepcarbon.net/deep-carbon-observatory-decade-discovery |access-date=13 December 2019 |archive-date=17 December 2019 |archive-url=https://web.archive.org/web/20191217174901/https://deepcarbon.net/deep-carbon-observatory-decade-discovery |url-status=dead }}</ref>]]
Peridotite is the dominant rock of the Earth's mantle above a depth of about 400&nbsp;km; below that depth, olivine is converted to the higher-pressure mineral [[wadsleyite]].<ref>{{cite journal |last1=Bercovici |first1=David |last2=Karato |first2=Shun-ichiro |title=Whole-mantle convection and the transition-zone water filter |journal=Nature |date=September 2003 |volume=425 |issue=6953 |pages=39–44 |doi=10.1038/nature01918|pmid=12955133 |bibcode=2003Natur.425...39B |s2cid=4428456 }}</ref>

Oceanic plates consist of up to about 100&nbsp;km of peridotite covered by a thin crust. The crust, commonly about 6&nbsp;km thick, consists of basalt, gabbro, and minor sediments. The peridotite below the ocean crust, "abyssal peridotite," is found on the walls of rifts in the deep sea floor.<ref name="refname" >{{cite journal |last1=Dick |first1=H. J. B. |title=Abyssal peridotites, very slow spreading ridges and ocean ridge magmatism |journal=Geological Society, London, Special Publications |date=1989 |volume=42 |issue=1 |pages=71–105 |doi=10.1144/GSL.SP.1989.042.01.06|bibcode=1989GSLSP..42...71D |s2cid=129660369 }}</ref> Oceanic plates are usually subducted back into the mantle in [[Subduction|subduction zones]]. However, pieces can be emplaced into or overthrust on [[continental crust]] by a process called [[obduction]], rather than carried down into the mantle. The emplacement may occur during [[orogeny|orogenies]], as during collisions of one continent with another or with an [[island arc]]. The pieces of oceanic plates emplaced within continental crust are referred to as [[ophiolites]]. Typical ophiolites consist mostly of peridotite plus associated rocks such as [[gabbro]], [[pillow basalt]], diabase sill-and-dike complexes, and red chert.{{sfn|Philpotts|Ague|2009|pp=370–374}}<ref>{{cite journal |last1=Dilek |first1=Y. |last2=Furnes |first2=H. |title=Ophiolites and Their Origins |journal=Elements |date=1 April 2014 |volume=10 |issue=2 |pages=93–100 |doi=10.2113/gselements.10.2.93|bibcode=2014Eleme..10...93D }}</ref> ''Alpine peridotite'' or ''orogenic peridotite massif'' is an older term for an ophiolite emplaced in a mountain belt during a continent-continent plate collision.{{sfn|Philpotts|Ague|2009|p=371}}<ref>{{cite journal |last1=Piccardo |first1=Giovanni B. |last2=Guarnieri |first2=Luisa |title=Alpine peridotites from the Ligurian Tethys: an updated critical review |journal=International Geology Review |date=July 2010 |volume=52 |issue=10–12 |pages=1138–1159 |doi=10.1080/00206810903557829|bibcode=2010IGRv...52.1138P |s2cid=128877324 }}</ref><ref>{{cite journal |last1=Spengler |first1=Dirk |last2=van Roermund |first2=Herman L. M. |last3=Drury |first3=Martyn R. |last4=Ottolini |first4=Luisa |last5=Mason |first5=Paul R. D. |last6=Davies |first6=Gareth R. |title=Deep origin and hot melting of an Archaean orogenic peridotite massif in Norway |journal=Nature |date=April 2006 |volume=440 |issue=7086 |pages=913–917 |doi=10.1038/nature04644|pmid=16612379 |bibcode=2006Natur.440..913S |s2cid=4419956 }}</ref>

Peridotites also occur as fragments ([[xenolith]]s) carried up by magmas from the mantle. Among the rocks that commonly include peridotite xenoliths are [[basalt]] and [[kimberlite]].<ref name="padovani-reid-1989">{{cite journal |last1=Padovani |first1=Elaine R. |last2=Reid |first2=Mary R. |title=Field guide to Kilbourne Hole maar, Dona Ana County, New Mexico |journal=New Mexico Bureau of Mines and Mineral Resources Memoir |date=1989 |volume=46 |pages=174–185}}</ref> Although [[kimberlite]] is a variant of peridotite, kimberlite is also considered as [[breccia]]ted volcanic material as well,<ref name=":0" /> which is why it is referred to as a source of peridotite xenoliths. Peridotite xenoliths contain osmium and other elements whose [[stable isotope ratio]]s provide clues on the formation and evolution of the Earth's mantle.<ref>{{cite journal |last1=Meisel |first1=Thomas |last2=Walker |first2=Richard J |last3=Irving |first3=Anthony J |last4=Lorand |first4=Jean-Pierre |title=Osmium isotopic compositions of mantle xenoliths: a global perspective |journal=Geochimica et Cosmochimica Acta |date=April 2001 |volume=65 |issue=8 |pages=1311–1323 |doi=10.1016/S0016-7037(00)00566-4|bibcode=2001GeCoA..65.1311M }}</ref><ref>{{cite journal |last1=Walker |first1=R.J |last2=Carlson |first2=R.W |last3=Shirey |first3=S.B |last4=F.R |first4=Boyd |title=Os, Sr, Nd, and Pb isotope systematics of southern African peridotite xenoliths: Implications for the chemical evolution of subcontinental mantle |journal=Geochimica et Cosmochimica Acta |date=July 1989 |volume=53 |issue=7 |pages=1583–1595 |doi=10.1016/0016-7037(89)90240-8|bibcode=1989GeCoA..53.1583W }}</ref> Such xenoliths originate from depths of up to nearly {{convert|200|km||sp=us}}<ref>{{cite journal |last1=Burgess |first1=S. R. |last2=Harte |first2=Ben |title=Tracing Lithosphere Evolution through the Analysis of Heterogeneous G9-G10 Garnets in Peridotite Xenoliths, II: REE Chemistry |journal=Journal of Petrology |date=1 March 2004 |volume=45 |issue=3 |pages=609–633 |doi=10.1093/petrology/egg095|doi-access=free }}</ref> or more.<ref>{{cite journal |last1=Ave Lallemant |first1=H.G. |last2=Mercier |first2=J-C.C. |last3=Carter |first3=N.L. |last4=Ross |first4=J.V. |title=Rheology of the upper mantle: Inferences from peridotite xenoliths |journal=Tectonophysics |date=December 1980 |volume=70 |issue=1–2 |pages=85–113 |doi=10.1016/0040-1951(80)90022-0|bibcode=1980Tectp..70...85A }}</ref>

The volcanic equivalent of peridotites are [[komatiite]]s, which were mostly erupted early in the Earth's history and are rare in rocks younger than [[Archean]] in age.<ref>{{cite journal |last1=Herzberg |first1=Claude |last2=Condie |first2=Kent |last3=Korenaga |first3=Jun |title=Thermal history of the Earth and its petrological expression |journal=Earth and Planetary Science Letters |date=15 March 2010 |volume=292 |issue=1–2 |pages=79–88 |doi=10.1016/j.epsl.2010.01.022|bibcode=2010E&PSL.292...79H |s2cid=12612486 }}</ref>

Small pieces of peridotite have been found in lunar breccias.<ref>{{cite journal |last1=Anderson |first1=A. T. |title=The Texture and Mineralogy of Lunar Peridotite, 15445,10 |journal=The Journal of Geology |date=March 1973 |volume=81 |issue=2 |pages=219–226 |doi=10.1086/627837|bibcode=1973JG.....81..219A |s2cid=128747551 }}</ref>

The rocks of the peridotite family are uncommon at the surface and are highly unstable, because olivine reacts quickly with water at typical temperatures of the upper crust and at the Earth's surface. Many, if not most, surface outcrops have been at least partly altered to [[serpentinite]], a process in which the pyroxenes and olivines are converted to green [[Serpentine group|serpentine]].<ref name=Nesse2000/> This hydration reaction involves considerable increase in volume with concurrent deformation of the original textures.<ref name=Mevel2003>{{cite journal |last1=Mével |first1=Catherine |title=Serpentinization of abyssal peridotites at mid-ocean ridges |journal=Comptes Rendus Geoscience |date=September 2003 |volume=335 |issue=10–11 |pages=825–852 |doi=10.1016/j.crte.2003.08.006|bibcode=2003CRGeo.335..825M |url=https://comptes-rendus.academie-sciences.fr/geoscience/articles/10.1016/j.crte.2003.08.006/ }}</ref> Serpentinites are mechanically weak and so flow readily within the earth.<ref>{{cite journal |last1=Vannucchi |first1=Paola |last2=Morgan |first2=Jason |last3=Polonia |first3=Alina |last4=Molli |first4=Giancarlo |title=How serpentine peridotites can leak through subduction channels |date=23 March 2020 |doi=10.5194/egusphere-egu2020-10250 |journal=EGU General Assembly 2020|page=10250 |bibcode=2020EGUGA..2210250V |s2cid=225971151 |doi-access=free }}</ref> Distinctive plant communities grow in soils developed on serpentinite, because of the unusual composition of the underlying rock.<ref name="Presidio">{{cite web |title=Serpentinite |url=https://www.nps.gov/prsf/learn/nature/serpentinite.htm |website=Presidio of San Francisco |publisher=National Park Service |access-date=3 September 2021}}</ref> One mineral in the serpentine group, [[chrysotile]], is a type of asbestos.{{sfn|Nesse|2000|pp=241–242}}