serpentinite

{{main article|Serpentinization}}

Serpentinite is formed by near to complete serpentinization of mafic or ultramafic rocks.{{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 }} Serpentinite is formed from mafic rock that is 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 zones.{{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 }}

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.{{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}} Accessory minerals, present in small quantities, include awaruite, other native metal minerals, and sulfide minerals.{{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}}Image:Gros Morne moho.jpg, Newfoundland. Ophiolites characteristically have a serpentinite component.]]

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:

:3 Fe2SiO4 + 2 H2O -> 2 Fe3O4 + 3 SiO2 + 2 H2

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}}.

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

In the Schikorr reaction, the two {{H+}} reduced into {{chem2|H2}} are these from two {{chem2|OH-}} anions, 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 activity in the deep subsurface environment.{{cn|date=January 2024}}

{{Main articles|Hydrothermal vent|Mud volcano}}

File:Expl2224 - Flickr - NOAA Photo Library.jpg spire in the Lost City hydrothermal field]]

Deep sea hydrothermal vents located on serpentinite close to the axis of mid-ocean ridges generally resemble black smokers 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 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 minerals and brucite. Lush 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}}. Sepiolite deposits on mid-ocean ridges may have formed through serpentinite-driven hydrothermal activity.{{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/ }} However, geologists continue to debate whether serpentinization alone can account for the heat flux from the Lost City field.{{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}}

The forearc of the Marianas subduction zone hosts large serpentinite mud volcanoes, which erupt serpentinite mud that rises through faults from the underlying serpentinized forearc mantle. Study of these mud volcanoes gives insights into subduction processes, and the high pH fluids emitted at the volcanoes support a microbial community.{{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}}

Experimental drilling into the gabbro layer of oceanic crust near mid-ocean ridges has demonstrated the presence of a sparse population of hydrocarbon-degrading bacteria. These may feed on hydrocarbons produced by serpentinization of the underlying ultramafic rock.{{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 }}{{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}}

Serpentinite thermal vents are a candidate for the environment in which life on Earth originated. Most of the chemical reactions necessary to synthesize acetyl-CoA, essential to basic biochemical pathways of life, take place during serpentinization.{{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 }} The sulfide-metal clusters that activate many enzymes resemble sulfide minerals formed during serpentinization.{{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}}

File:Landscape, south of New Caledonia.jpg]]

{{main|Serpentine soil}}

Soil cover over serpentinite bedrock tends to be thin or absent. Soil with serpentine is poor in calcium and other major plant nutrients, but rich in elements toxic to plants such as chromium and nickel.[http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Notes/serpentine.html "CVO Website - Serpentine and serpentinite"] {{webarchive|url=https://web.archive.org/web/20111019015059/http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Notes/serpentine.html |date=19 October 2011 }}, USGS/NPS Geology in the Parks Website, September 2001, accessed 27 February 2011. Some species of plants, such as Clarkia franciscana and certain species of manzanita, are adapted to living on serpentinite outcrops. However, because serpentinite outcrops are few and isolated, their plant communities are ecological islands and these distinctive species are often highly endangered.{{cite web |title=Serpentinite |url=https://www.nps.gov/prsf/learn/nature/serpentinite.htm |access-date=3 September 2021 |website=Presidio of San Francisco |publisher=National Park Service}} On the other hand, plant communities adapted to living on the serpentine outcrops of New Caledonia resist displacement by introduced species that are poorly adapted to this environment.{{cite web|url=http://www.futura-sciences.com/fr/doc/t/zoologie-1/r/nouvelle-caledonie/d/la-faune-et-la-flore-de-nouvelle-caledonie_468/c3/221/p2/ |title=La flore de Nouvelle-Calédonie – Première partie |website=Futura-sciences.com |date=2004-08-18 |access-date=2013-01-30}}

Serpentine soils are widely distributed on Earth, in part mirroring the distribution of ophiolites and other serpentine bearing rocks.{{Cite journal |title=6 Serpentine Soil Distributions and Environmental Influences |url=https://academic.oup.com/book/41004/chapter-abstract/349244500?redirectedFrom=fulltext |access-date=2022-11-20 |website=academic.oup.com| date=2007 | doi=10.1093/oso/9780195165081.003.0010 | last1=Alexander | first1=Earl B. | last2=Coleman | first2=Roger G. | last3=Keeler-Wolfe | first3=Todd | last4=Harrison | first4=Susan P. | isbn=978-0-19-516508-1 | url-access=subscription }} There are outcroppings of serpentine soils in the Balkan Peninsula, Turkey, the island of Cyprus, the Alps, Cuba, and New Caledonia. In North America, serpentine soils also are present in small but widely distributed areas on the eastern slope of the Appalachian Mountains in the eastern United States, and in the Pacific Ranges of Oregon and California.{{citation needed|date=July 2022}}

Notable occurrences of serpentinite are found at Thetford Mines, Quebec; Lake Valhalla, New Jersey; Gila County, Arizona; Lizard complex, Lizard Point, Cornwall; and in localities in Greece, Italy, and other parts of Europe.{{cite book |last1=Sinkankas |first1=John |title=Mineralogy for amateurs. |date=1964 |publisher=Van Nostrand |isbn=0442276249 |location=Princeton, N.J. |pages=149–480}} Notable ophiolites containing serpentinite include the Semail Ophiolite of Oman, the Troodos Ophiolite of Cyprus, the Newfoundland ophiolites, and the Main Ophiolite Belt of New Guinea.{{cite book |last1=Philpotts |first1=Anthony R. |last2=Ague |first2=Jay J. |title=Principles of igneous and metamorphic petrology |date=2009 |publisher=Cambridge University Press |location=Cambridge, UK |isbn=9780521880060 |edition=2nd |page=371}}

Another occurrence of serpentinite is in Chester County, Pennsylvania.

File:Zwei trinkbecher, zoeblitz.jpg in the Erzgebirgskreis]]

File:College Hall U Penn.JPG]]

Serpentine group minerals have a Mohs hardness of 2.5 to 3.5, so serpentinite is easily carved.{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |page=239}} Grades of serpentinite higher in calcite, along with the verd antique (breccia form of serpentinite), have historically been used as decorative stones for their marble-like qualities. College Hall at the University of Pennsylvania, for example, is constructed out of serpentine. Popular sources in Europe before contact with the Americas were the mountainous Piedmont region of Italy and Larissa, Greece.Ashurst, John. Dimes, Francis G. Conservation of building and decorative stone. Elsevier Butterworth-Heinemann, 1990, p. 51.

Serpentinites are used in many ways in the arts and crafts. For example, the rock has been turned in Zöblitz in Saxony for several hundred years.Eva Maria Hoyer: Sächsischer Serpentin: ein Stein und seine Verwendung. Edition Leipzig, Leipzig 1996, pp. 20–22.

{{Anchor|Inuit|Qulliq}}The Inuit and other indigenous people of the Arctic areas and less so of southern areas used the carved bowl shaped serpentinite qulliq or kudlik lamp with wick, to burn oil or fat to heat, make light and cook with. The Inuit made tools and more recently carvings of animals for commerce.{{cite journal |last1=Kerr |first1=A. |last2=Squires |first2=G.C. |title=Serpentinites and associated rock types near Hopedale, Nunatsiavut: Potential for artisanal carving-stone resources |journal=Geological Survey Report |volume=19 |issue=1 |pages=39–57 |url=https://www.gov.nl.ca/iet/files/mines-geoscience-publications-currentresearch-2019-kerr-2019.pdf |access-date=3 September 2021 |publisher=Newfoundland and Labrador Department of Natural Resources}}

File:Serpentinite_Walrus_2012.jpg|Magnetic serpentine walrus

File:Qulliq_1999-04-01.jpg|Inuit Elder tending the Qulliq, a ceremonial oil lamp made of serpentinite.

A variety of chlorite talc schist associated with Alpine serpentinite is found in Val d'Anniviers, Switzerland and was used for making "ovenstones" ({{langx|de|Ofenstein}}), a carved stone base beneath a cast iron stove.[http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleForFree.cfm?doi=CA8987405232&JournalCode=CA Talcose-schist from Canton Valais. By Thomags Bonney, (Geol. Mag., 1897, N.S., [iv], 4, 110--116) abstract]

Serpentinite has a significant amount of bound water, hence it contains abundant hydrogen atoms able to slow down neutrons by elastic collision (neutron thermalization process). Because of this, serpentinite can be used as dry filler inside steel jackets in some designs of nuclear reactors. For example, in RBMK series, as at Chernobyl, it was used for top radiation shielding to protect operators from escaping neutrons.{{Cite web| last = Lithuanian Energy Institute| title = Design of structures, components, equipments and systems| work = Ignalina Source Book| access-date = 2011-05-28| date = 2011-05-28| url = http://www.lei.lt/insc/sourcebook/sob3/sob33.html| archive-date = 9 October 2011| archive-url = https://web.archive.org/web/20111009041613/http://www.lei.lt/insc/sourcebook/sob3/sob33.html| url-status = dead}} Serpentine can also be added as aggregate to special concrete used in nuclear reactor shielding to increase the concrete density ({{convert|2.6|g/cm3|abbr=on}}) and its neutron capture cross section.{{Cite conference| last1 = Aminian| first1 = A.| last2 = Nematollahi| first2 = M.R.| last3 = Haddad| first3 = K.| last4 = Mehdizadeh| first4 = S.| date = 3–8 June 2007| title = Determination of shielding parameters for different types of concretes by Monte Carlo methods| location = Istanbul, Turkey| conference = ICENES 2007: International Conference on Emerging Nuclear Energy Systems. Session 12B: Radiation effects| pages = 7| url = http://www.icenes2007.org/icenes_proceedings/manuscripts.pdf/Session%2012B/DETERMINATION%20OF.pdf| access-date = 28 May 2011| archive-date = 3 March 2016| archive-url = https://web.archive.org/web/20160303170929/http://www.icenes2007.org/icenes_proceedings/manuscripts.pdf/Session%2012B/DETERMINATION%20OF.pdf| url-status = dead}}{{Cite journal| last = Abulfaraj| first = Waleed H.|author2=Salah M. Kamal| title = Evaluation of ilmenite serpentine concrete and ordinary concrete as nuclear reactor shielding| journal = Radiation Physics and Chemistry| volume = 44| issue = 1–2| pages = 139–148| doi = 10.1016/0969-806X(94)90120-1| issn = 0969-806X|bibcode = 1994RaPC...44..139A | year = 1994}}

{{Main article|Carbon sequestration}}

Because it readily absorbs carbon dioxide, serpentinite may be of use for sequestering atmospheric carbon dioxide.{{cite journal |last1=Farhang |first1=F. |last2=Oliver |first2=T.K. |last3=Rayson |first3=M.S. |last4=Brent |first4=G.F. |last5=Molloy |first5=T.S. |last6=Stockenhuber |first6=M. |last7=Kennedy |first7=E.M. |title=Dissolution of heat activated serpentine for CO₂ sequestration: The effect of silica precipitation at different temperature and pH values |journal=Journal of CO₂ Utilization |date=March 2019 |volume=30 |pages=123–129 |doi=10.1016/j.jcou.2019.01.009|s2cid=104424416 }} To speed up the reaction, serpentinite may be reacted with carbon dioxide at elevated temperature in carbonation reactors. Carbon dioxide may also be reacted with alkaline mine waste from serpentine deposits, or carbon dioxide may be injected directly into underground serpentinite formations.{{cite journal |last1=Power |first1=I. M. |last2=Wilson |first2=S. A. |last3=Dipple |first3=G. M. |title=Serpentinite Carbonation for CO₂ Sequestration |journal=Elements |date=1 April 2013 |volume=9 |issue=2 |pages=115–121 |doi=10.2113/gselements.9.2.115|bibcode=2013Eleme...9..115P }} Serpentinite may also be used as a source of magnesium in conjunction with electrolytic cells for CO₂ scrubbing.{{cite journal |last1=Li |first1=Wenzhi |last2=Li |first2=Wen |last3=Li |first3=Baoqing |last4=Bai |first4=Zongqing |title=Electrolysis and heat pretreatment methods to promote CO₂ sequestration by mineral carbonation |journal=Chemical Engineering Research and Design |date=February 2009 |volume=87 |issue=2 |pages=210–215 |doi=10.1016/j.cherd.2008.08.001 |bibcode=2009CERD...87..210L |language=en}}

It is the state rock of California, USA and the California Legislature specified that serpentine was "the official State Rock and lithologic emblem." In 2010, a bill was introduced which would have removed serpentine's special status as state rock due to it potentially containing chrysotile asbestos.{{cite news|last1=Fimrite|first1=Peter|title=Geologists protest bill to remove state rock|url=https://www.sfgate.com/news/article/Geologists-protest-bill-to-remove-state-rock-3258944.php|access-date=17 April 2018|work=San Francisco Chronicle|date=16 July 2010}} The bill met with resistance from some California geologists, who noted that the chrysotile present is not hazardous unless it is mobilized in the air as dust.{{cite web|last1=Frazell|first1=Julie|last2=Elkins|first2=Rachel|last3=O'Geen|first3=Anthony|last4=Reynolds|first4=Robert|last5=Meyers|first5=James|title=Facts about Serpentine Rock and Soil Containing Asbestos in California|url=http://anrcatalog.ucanr.edu/pdf/8399.pdf|website=ANR Catalog|publisher=University of California Division of Agriculture and Natural Resources|access-date=17 April 2018}}

{{Update inline|reason=Is serpentine still the state rock of California? Did the 2010 repeal attempt succeed or fail?|date=March 2022}}

• {{annotated link|Hydrogen cycle}}
• {{annotated link|Nephrite}}
• {{annotated link|Soapstone}}

{{Reflist}}

{{commons category|Serpentinite}}

• [http://www.lostcity.washington.edu/story/Serpentinization] The Lost City hydrothermal field, Mid-Atlantic Ridge: serpentinization, the driving force of the system.
• [http://www.pnas.org/cgi/content/full/101/35/12818 H₂-rich fluids from serpentinization: Geochemical and biotic implications]: Proceedings of the National Academy of Sciences.

{{Rock type}}

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Category:Serpentine group

Category:Metamorphic petrology

Category:Metamorphic rocks