Editing Serpentinite (section)

== Formation and mineralogy ==
{{main article|Serpentinization}}
Serpentinite is formed by near to complete [[serpentinization]] of [[mafic]] or [[ultramafic rock]]s.<ref>{{Cite book |title=Introduction to Mineralogy and Petrology |url=https://www.sciencedirect.com/book/9780128205853/introduction-to-mineralogy-and-petrology |access-date=2022-11-20 |isbn=9780128205853 |language=en |last1=Haldar |first1=Swapan Kumar |date=27 July 2020 |publisher=Elsevier Science }}</ref> Serpentinite is formed from mafic rock that is [[mineral hydration|hydrated]] by [[carbon dioxide]]-deficient [[sea water]] that is pressed into the rock at great depths below the ocean floor.{{sfn|Moody|1976|p=136}} This occurs at [[mid-ocean ridges]] and in the [[forearc]] mantle of [[subduction zone]]s.<ref name="Roberts-2012" /><ref name="Albers-2021">{{Cite journal |last1=Albers |first1=Elmar |last2=Bach |first2=Wolfgang |last3=Pérez-Gussinyé |first3=Marta |last4=McCammon |first4=Catherine |last5=Frederichs |first5=Thomas |date=2021 |title=Serpentinization-Driven H2 Production From Continental Break-Up to Mid-Ocean Ridge Spreading: Unexpected High Rates at the West Iberia Margin |journal=Frontiers in Earth Science |volume=9 |page=487 |doi=10.3389/feart.2021.673063 |bibcode=2021FrEaS...9..487A |issn=2296-6463|doi-access=free }}</ref>

The final mineral composition of serpentinite is usually dominated by [[antigorite]],  [[lizardite]], [[chrysotile]] (minerals of the [[serpentine subgroup]]), and [[magnetite]] ({{Chem2|link=Magnetite|Fe3O4}}), with [[brucite]] ({{Chem2|link=Brucite|Mg(OH)2}}) less commonly present. Lizardite, chrysotile, and antigorite all have approximately the formula {{chem2|Mg3(Si2O5)(OH)4}} or {{chem2|(Mg(2+), Fe(2+))3Si2O5(OH)4}}, but differ in minor components and in form.<ref name="Roberts-2012">{{Cite book|last1=Roberts|first1=B. A.|url=https://books.google.com/books?id=Abb1CAAAQBAJ&dq=Lizardite&pg=PA11|title=The Ecology of Areas with Serpentinized Rocks: A World View|last2=Proctor|first2=J.|date=2012-12-06|publisher=Springer Science & Business Media|isbn=978-94-011-3722-5|language=en|page=8}}</ref> Accessory minerals, present in small quantities, include [[awaruite]], other native metal minerals, and [[sulfide mineral]]s.<ref name="Moody-1976">{{cite journal |last1=Moody |first1=Judith B. |date=April 1976 |title=Serpentinization: a review |journal=Lithos |volume=9 |issue=2 |pages=125–138 |bibcode=1976Litho...9..125M |doi=10.1016/0024-4937(76)90030-X}}</ref>[[Image:Gros Morne moho.jpg|thumb|Ophiolite of the [[Gros Morne National Park]], [[Newfoundland (island)|Newfoundland]]. Ophiolites characteristically have a serpentinite component.]]

=== Hydrogen production ===
The [[serpentinization]] reaction involving the transformation of [[fayalite]] (Fe-end member of [[olivine]]) by water into [[magnetite]] and [[quartz]] also produces molecular [[hydrogen]] {{chem2|H2}} according to the following reaction:
:<chem>3 Fe2SiO4 + 2 H2O -> 2 Fe3O4 + 3 SiO2 + 2 H2</chem>

This reaction closely resembles the [[Schikorr reaction]] also producing hydrogen gas by [[oxidation]] of Fe{{sup|2+}} ions into Fe{{sup|3+}} ions by the protons {{H+}} of water. Two {{H+}} are then reduced into {{chem2|H2}}.

:<chem>3 Fe(OH)2 -> Fe3O4 + 2 H2O + H2</chem>

In the Schikorr reaction, the two {{H+}} reduced into {{chem2|H2}} are these from two {{chem2|OH-}} [[anion]]s, then transformed into two oxide anions ({{chem2|O(2-)}}) directly incorporated into the magnetite [[crystal lattice]] while the water in excess is liberated as a reaction by-product.

Hydrogen produced by the serpentinization reaction is important because it can fuel [[Microbial metabolism|microbial activity]] in the deep subsurface environment.{{cn|date=January 2024}}

=== Hydrothermal vents and mud volcanoes ===
{{Main articles|Hydrothermal vent|Mud volcano}}
[[File:Expl2224 - Flickr - NOAA Photo Library.jpg|thumb|A white [[Carbonate mineral|carbonate]] spire in the [[Lost City Hydrothermal Field|Lost City hydrothermal field]]]]
Deep sea [[hydrothermal vent]]s located on serpentinite close to the axis of [[mid-ocean ridge]]s generally resemble [[black smoker]]s located on [[basalt]], but emit complex [[hydrocarbon]] molecules. The Rainbow field of the [[Mid-Atlantic Ridge]] is an example of such hydrothermal vents. Serpentinization alone cannot provide the heat supply for these vents, which must be driven mostly by [[magmatism]]. However, the [[Lost City Hydrothermal Field]], located off the axis of the Mid-Atlantic Ridge, may be driven solely by heat of serpentinization. Its vents are unlike black smokers, emitting relatively cool fluids ({{convert|40 to 75|C||sp=us}}) that are highly [[Alkalinity|alkaline]], high in [[magnesium]], and low in [[hydrogen sulfide]]. The vents build up very large chimneys, up to {{convert|60|m||sp=us}} in height, composed of [[carbonate mineral]]s and brucite. Lush [[Microbial population biology|microbial communities]] are associated with the vents. Though the vents themselves are not composed of serpentinite, they are hosted in serpentinite estimated to have formed at a temperature of about {{convert|200|C||sp=us}}.<ref name="Allen-2004" /> [[Sepiolite]] deposits on mid-ocean ridges may have formed through serpentinite-driven [[Hydrothermal circulation|hydrothermal activity]].<ref name="Mével-2003">{{cite journal |last1=Mével |first1=Catherine |date=September 2003 |title=Serpentinization of abyssal peridotites at mid-ocean ridges |journal=Comptes Rendus Geoscience |volume=335 |issue=10–11 |pages=825–852 |bibcode=2003CRGeo.335..825M |doi=10.1016/j.crte.2003.08.006|url=https://comptes-rendus.academie-sciences.fr/geoscience/articles/10.1016/j.crte.2003.08.006/ }}</ref> However, geologists continue to debate whether serpentinization alone can account for the [[heat flux]] from the Lost City field.<ref name="Allen-2004">{{cite journal |last1=Allen |first1=Douglas E. |last2=Seyfried |first2=W.E. |title=Serpentinization and heat generation: constraints from Lost City and Rainbow hydrothermal systems 1 1Associate editor: J. C. Alt |journal=Geochimica et Cosmochimica Acta |date=March 2004 |volume=68 |issue=6 |pages=1347–1354 |doi=10.1016/j.gca.2003.09.003}}</ref>

The [[forearc]] of the [[Mariana Trench|Marianas]] [[subduction]] zone hosts large serpentinite [[mud volcano]]es, which erupt serpentinite mud that rises through [[Fault (geology)|faults]] from the underlying serpentinized forearc [[Mantle (geology)|mantle]]. Study of these mud volcanoes gives insights into subduction processes, and the high [[pH]] fluids emitted at the volcanoes support a [[Microbial consortium|microbial community]].<ref name="Fryer-2012">{{cite journal |last1=Fryer |first1=Patricia |title=Serpentinite Mud Volcanism: Observations, Processes, and Implications |journal=Annual Review of Marine Science |date=15 January 2012 |volume=4 |issue=1 |pages=345–373 |doi=10.1146/annurev-marine-120710-100922 |pmid=22457979 |bibcode=2012ARMS....4..345F |language=en |issn=1941-1405}}</ref><ref name="Albers-2021" />
Experimental drilling into the [[gabbro]] layer of [[oceanic crust]] near mid-ocean ridges has demonstrated the presence of a sparse population of [[Microbial biodegradation|hydrocarbon-degrading]] [[bacteria]]. These may feed on hydrocarbons produced by serpentinization of the underlying [[ultramafic rock]].<ref>{{cite journal |last1=Mason |first1=Olivia U. |last2=Nakagawa |first2=Tatsunori |last3=Rosner |first3=Martin |last4=Van Nostrand |first4=Joy D. |last5=Zhou |first5=Jizhong |last6=Maruyama |first6=Akihiko |last7=Fisk |first7=Martin R. |last8=Giovannoni |first8=Stephen J. |title=First Investigation of the Microbiology of the Deepest Layer of Ocean Crust |journal=PLOS ONE|date=5 November 2010 |volume=5 |issue=11 |pages=e15399 |pmc=2974637 |  doi=10.1371/journal.pone.0015399|pmid=21079766 |bibcode=2010PLoSO...515399M |doi-access=free }}</ref><ref>{{cite news |last1=Marshall |first1=Michael |title=Life is found in deepest layer of Earth's crust |url=https://www.newscientist.com/article/mg20827874-800-life-is-found-in-deepest-layer-of-earths-crust/?ignored=irrelevant |access-date=3 December 2021 |work=New Scientist |date=17 November 2010}}</ref>

====Potential 'cradle of life'====
Serpentinite thermal vents are a candidate for the environment in which life on Earth originated.<ref name="Fryer-2012"/> Most of the chemical reactions necessary to synthesize [[acetyl-CoA]], essential to basic biochemical pathways of life, take place during serpentinization.<ref>{{cite journal |last1=Martin |first1=William |author-link1=William F. Martin
|last2=Russell |first2=Michael J |author-link2=Michael Russell (scientist)|title=On the origin of biochemistry at an alkaline hydrothermal vent |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |date=29 October 2007 |volume=362 |issue=1486 |pages=1887–1926 |doi=10.1098/rstb.2006.1881|pmid=17255002 |pmc=2442388 }}</ref> The sulfide-metal clusters that activate many [[enzyme]]s resemble sulfide minerals formed during serpentinization.<ref>{{cite journal |last1=McCollom |first1=T. M. |last2=Seewald |first2=J. S. |title=Serpentinites, Hydrogen, and Life |journal=Elements |date=1 April 2013 |volume=9 |issue=2 |pages=129–134 |doi=10.2113/gselements.9.2.129 |bibcode=2013Eleme...9..129M |citeseerx=10.1.1.852.2089 |url=https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.852.2089&rep=rep1&type=pdf |access-date=5 September 2021}}</ref>