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A rock of serpentinite from the Maurienne valley, Savoie, French Alps

A rock of serpentinite from the Maurienne valley, Savoie, French Alps

Sample of serpentinite from the Golden Gate National Recreation Area, California, United States

Sample of serpentinite from the Golden Gate National Recreation Area, California, United States

Chromitic serpentinite  (7.9 cm across), Styria Province, Austria. Protolith was  a Proterozoic-Early Paleozoic upper mantle dunite peridotite that has been multiply metamorphosed during the Devonian, Permian, and Mesozoic.

Chromitic serpentinite (7.9 cm across), Styria Province, Austria. Protolith was a Proterozoic-Early Paleozoic upper mantle dunite peridotite that has been multiply metamorphosed during the Devonian, Permian, and Mesozoic.

Tightly folded serpentinite from the  Tux Alps, Austria. Closeup view about 30cm × 20cm.

Tightly folded serpentinite from the Tux Alps, Austria. Closeup view about 30cm × 20cm.

Serpentinite is a rock composed of one or more serpentine group minerals, the name originating from the similarity of the texture of the rock to that of the skin of a snake.[1] Minerals in this group, which are rich in magnesium and water, light to dark green, greasy looking and slippery feeling, are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle. The mineral alteration is particularly important at the sea floor at tectonic plate boundaries.[2]

Formation and petrology

Serpentinization is a geological low-temperature metamorphic process involving heat and water in which low-silica mafic and ultramafic rocks are oxidized (anaerobic oxidation of Fe2+ by the protons of water leading to the formation of H2) and hydrolyzed with water into serpentinite. Peridotite, including dunite, at and near the seafloor and in mountain belts is converted to serpentine, brucite, magnetite, and other minerals — some rare, such as awaruite (Ni3Fe), and even native iron. In the process large amounts of water are absorbed into the rock increasing the volume, reducing the density and destroying the structure.[3]

The density changes from 3.3 to 2.7 g/cm3 with a concurrent volume increase on the order of 30-40%. The reaction is highly exothermic and rock temperatures can be raised by about 260 °C (500 °F),[3] providing an energy source for formation of non-volcanic hydrothermal vents. The magnetite-forming chemical reactions produce hydrogen gas under anaerobic conditions prevailing deep in the mantle, far from the Earth's atmosphere. Carbonates and sulfates are subsequently reduced by hydrogen and form methane and hydrogen sulfide. The hydrogen, methane, and hydrogen sulfide provide energy sources for deep sea chemotroph microorganisms.[3]

Serpentinite reactions

Serpentinite is formed from olivine via several reactions, some of which are complementary. Olivine is a solid solution between the magnesium-endmember forsterite and the iron-endmember fayalite. Serpentinite reaction 1a and 1b, below, exchange silica between forsterite and fayalite to form serpentine group minerals and magnetite. These are highly exothermic reactions.

Fayalite3 Fe2SiO4
water2 H2Omagnetite2 Fe3O4
aqueous silica3 SiO2
hydrogen2 H2
**(Reaction 1a)**
Forsterite3 Mg2SiO4
aqueous silicaSiO2
  • 4 H
serpentine2 Mg3Si2O5(OH)4
**(Reaction 1b)**
Forsterite2 Mg2SiO4
water3 H2OserpentineMg3Si2O5(OH)4
**(Reaction 1c)**

Reaction 1c describes the hydration of olivine with water only to yield serpentine and Mg(OH)2 (brucite).[4] Serpentine is stable at high pH in the presence of brucite like calcium silicate hydrate, (C-S-H) phases formed along with portlandite (Ca(OH)2) in hardened Portland cement paste after the hydration of belite (Ca2SiO4), the artificial calcium equivalent of forsterite.

Analogy of reaction 1c with belite hydration in ordinary Portland cement:

Belite2 Ca2SiO4
water4 H2OC-S-H phase3 CaO · 2 SiO2· 3 H2O
**(Reaction 1d)**

After reaction, the poorly soluble reaction products (aqueous silica or dissolved magnesium ions) can be transported in solution out of the serpentinized zone by diffusion or advection.

A similar suite of reactions involves pyroxene-group minerals, though less readily and with complication of the additional end-products due to the wider compositions of pyroxene and pyroxene-olivine mixes. Talc and magnesian chlorite are possible products, together with the serpentine minerals antigorite, lizardite, and chrysotile. The final mineralogy depends both on rock and fluid compositions, temperature, and pressure. Antigorite forms in reactions at temperatures that can exceed 600 °C (1,112 °F) during metamorphism, and it is the serpentine group mineral stable at the highest temperatures. Lizardite and chrysotile can form at low temperatures very near the Earth's surface. Fluids involved in serpentinite formation commonly are highly reactive and may transport calcium and other elements into surrounding rocks; fluid reaction with these rocks may create metasomatic reaction zones enriched in calcium and called rodingites.

In the presence of carbon dioxide, however, serpentinitization may form either magnesite (MgCO3) or generate methane (CH4). It is thought that some hydrocarbon gases may be produced by serpentinite reactions within the oceanic crust.

carbon dioxideCO2serpentineMg3Si2O5(OH)4
**(Reaction 2a)**

or, in balanced form:

18 Mg2SiO4
  • 6 Fe
  • 26 H
2O + CO2→ 12 Mg3Si2O5(OH)4
  • 4 Fe
  • CH
**(Reaction 2a')**
carbon dioxideCO2serpentineMg3Si2O5(OH)4
**(Reaction 2b)**

Reaction 2a is favored if the serpentinite is Mg-poor or if there isn't enough carbon dioxide to promote talc formation. Reaction 2b is favored in highly magnesian compositions and low partial pressure of carbon dioxide.

The degree to which a mass of ultramafic rock undergoes serpentinisation depends on the starting rock composition and on whether or not fluids transport calcium, magnesium and other elements away during the process. If an olivine composition contains sufficient fayalite, then olivine plus water can completely metamorphose to serpentine and magnetite in a closed system. In most ultramafic rocks formed in the Earth's mantle, however, the olivine is about 90% forsterite endmember, and for that olivine to react completely to serpentine, magnesium must be transported out of the reacting volume.

Serpentinitization of a mass of peridotite usually destroys all previous textural evidence because the serpentine minerals are weak and behave in a very ductile fashion. However, some masses of serpentinite are less severely deformed, as evidenced by the apparent preservation of textures inherited from the peridotite, and the serpentinites may have behaved in a rigid fashion.

Hydrogen production by anaerobic oxidation of fayalite ferrous ions

Serpentine is the product of the reaction between water and fayalite's ferrous (Fe2+) ions.[5][6]


Considering three formula units of fayalite (Fe2(SiO4)) for the purpose of stoichiometry and reaction mass balance, four ferrous ions will undergo oxidation by water protons while the two remaining will stay unoxidised. Neglecting the orthosilicate anions not involved in the redox process, it is then possible to schematically write the two half-redox reactions as follows:

4 Fe2+
  • 2 H
2O → 4 Fe3+
  • 2 O
  • 2 H
**(Reaction 3c)**

The process is of interest because it generates hydrogen gas.

The two unoxidised ferrous (Fe2+) ions still available in the three formula units of fayalite finally combine with the four ferric (Fe3+) cations and additional available free oxide anions (O2−)(see below) to form two formula units of magnetite (Fe3O4).

Finally, considering the required rearrangement of the orthosilicate anions into free silica (SiO2) and free oxide anions (O2−), it is possible to write the complete reaction of anaerobic oxidation and hydrolysis of fayalite according to the following mass balance:

3 Fe2SiO4fayalite
2 H2Owater2 Fe3O4magnetite
3 SiO2quartz
2 H2hydrogen
**(Reaction 3d)**

This reaction resembles the Schikorr reaction observed in the anaerobic oxidation of the ferrous hydroxide in contact with water:

3 Fe(OH)2ferrous hydroxideFe3O4magnetite
2 H2Owater
**(Reaction 3e)**

Abiotic methane production on Mars by serpentinization

The presence of traces of methane in the atmosphere of Mars has been hypothesized to be a possible evidence for life on Mars if methane was produced by bacterial activity. Serpentinization has been proposed as an alternative non-biological source for the observed methane traces.[7][8]

Serpentinization on Enceladus

Using data from the Cassini probe flybys obtained in 2010–12, scientists were able to confirm that Saturn's moon Enceladus likely has a liquid water ocean beneath its frozen surface. A model suggests that the ocean on Enceladus has an alkaline pH of 11–12.[9] The high pH is interpreted to be a key consequence of serpentinization of chondritic rock, that leads to the generation of H2, a geochemical source of energy that can support both abiotic and biological synthesis of organic molecules.[9][10]

Impact on agriculture

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.[11]


Decorative stone in architecture

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.[12]

Carvingstone tools, oil lamp-known as the Qulliq and Inuit sculpture

Inuit and 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. Inuit made tools and more recently carvings of animals for commerce.

Swiss ovenstone

A variety of chlorite talc schist associated with Alpine serpentinite is found in Val d’Anniviers, Switzerland and was used for making "ovenstones" (Ger. Ofenstein), a carved stone base beneath a cast iron stove.[13]

Neutron shield in nuclear reactors

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 it was used for top radiation shielding to protect operators from escaping neutrons.[14] Serpentine can also be added as aggregate to special concrete used in nuclear reactor shielding to increase the concrete density (2.6 g/cm3) and its neutron capture cross section.[15][16]

Cultural references

It is the state rock of California, USA and the California Legislature specified that serpentine was "the official State Rock and lithologic emblem."[17] In 2010, a bill was introduced which would have removed serpentine's special status as state rock due to it potentially containing chrysotile asbestos.[18] 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.[19]

See also

  • Carbon sequestration

  • Cement chemist notation, also useful for silicate and oxide reactions in mineralogy

  • Chrysotile dehydration – The most commonly encountered form of asbestos

  • Common redox mineral buffer – FMQ: fayalite-magnetite-quartz

  • Geology of the Lizard peninsula

  • Hydration of belite in cement (analogous to forsterite hydration)

  • Lost City Hydrothermal Field – Hydrothermal field in the mid-Atlantic Ocean

  • Nephrite – A variety of jade

  • Schikorr reaction, involving also the formation of magnetite and hydrogen by a very similar mechanism

  • Serpentine soil, a soil derived from serpentine minerals

  • Serpentine subgroup, the main minerals comprising serpentinite

  • Soapstone

  • Talc carbonate

  • Hydrogen Cycle


Citation Linkbooks.google.comSchoenherr, Allan A. (11 July 2017). A Natural History of California: Second Edition. Univ of California Press. pp. 35–. ISBN 9780520295117. Retrieved 6 May 2017.
Sep 21, 2019, 8:40 PM
Citation Linkwww.theodora.com"Serpentine definition". Dictionary of Geology. Retrieved 23 October 2018.
Sep 21, 2019, 8:40 PM
Citation Linkwww.lostcity.washington.eduSerpentinization: The heat engine at Lost City and sponge of the oceanic crust
Sep 21, 2019, 8:40 PM
Citation Linkopenlibrary.orgColeman, Robert G. (1977). Ophiolites. Springer-Verlag. pp. 100–101. ISBN 978-3540082767.
Sep 21, 2019, 8:40 PM
Citation Linkwww.lostcity.washington.edu"Methane and hydrogen formation from rocks – Energy sources for life". Retrieved 6 November 2011.
Sep 21, 2019, 8:40 PM
Citation Link//www.ncbi.nlm.nih.gov/pubmed/15326313Sleep, N.H.; A. Meibom, Th. Fridriksson, R.G. Coleman, D.K. Bird (2004). "H2-rich fluids from serpentinization: Geochemical and biotic implications". Proceedings of the National Academy of Sciences of the United States of America. 101 (35): 12818–12823. Bibcode:2004PNAS..10112818S. doi:10.1073/pnas.0405289101. PMC 516479. PMID 15326313.CS1 maint: multiple names: authors list (link)
Sep 21, 2019, 8:40 PM
Citation Link//www.jstor.org/stable/27858733Baucom, Martin (March–April 2006). "Life on Mars?". American Scientist. 94 (2): 119–120. JSTOR 27858733.
Sep 21, 2019, 8:40 PM
Citation Linkwww.esa.intesa. "The methane mystery". European Space Agency. Retrieved 22 April 2019.
Sep 21, 2019, 8:40 PM
Citation Link//doi.org/10.1016%2Fj.gca.2015.04.017R. Glein, Christopher; Baross, John A.; Waite, Hunter (16 April 2015). "The pH of Enceladus' ocean". Geochimica et Cosmochimica Acta. 162: 202–219. arXiv:1502.01946. Bibcode:2015GeCoA.162..202G. doi:10.1016/j.gca.2015.04.017.
Sep 21, 2019, 8:40 PM
Citation Linkwww.space.comWall, Mike (7 May 2015). "Ocean on Saturn Moon Enceladus May Have Potential Energy Source to Support Life". Space.com. Retrieved 8 May 2015.
Sep 21, 2019, 8:40 PM
Citation Linkweb.archive.org"CVO Website - Serpentine and serpentinite" Archived 19 October 2011 at the Wayback Machine, USGS/NPS Geology in the Parks Website, September 2001, accessed 27 February 2011.
Sep 21, 2019, 8:40 PM
Citation Linkopenlibrary.orgAshurst, John. Dimes, Francis G. Conservation of building and decorative stone. Elsevier Butterworth-Heinemann, 1990, p. 51.
Sep 21, 2019, 8:40 PM
Citation Linkwww.rsc.orgTalcose-schist from Canton Valais. By Thomags Bonney, (Geol. Mag., 1897, N.S., [iv], 4, 110--116) abstract
Sep 21, 2019, 8:40 PM
Citation Linkwww.lei.ltLithuanian Energy Institute (28 May 2011). "Design of structures, components, equipments and systems". Ignalina Source Book. Retrieved 28 May 2011.
Sep 21, 2019, 8:40 PM
Citation Linkwww.icenes2007.orgAminian, A.; Nematollahi, M.R.; Haddad, K.; Mehdizadeh, S. (3–8 June 2007). Determination of shielding parameters for different types of concretes by Monte Carlo methods (PDF). ICENES 2007: International Conference on Emerging Nuclear Energy Systems. Session 12B: Radiation effects. Istanbul, Turkey. p. 7.
Sep 21, 2019, 8:40 PM
Citation Linkportal.issn.orgAbulfaraj, Waleed H.; Salah M. Kamal (1994). "Evaluation of ilmenite serpentine concrete and ordinary concrete as nuclear reactor shielding". Radiation Physics and Chemistry. 44 (1–2): 139–148. Bibcode:1994RaPC...44..139A. doi:10.1016/0969-806X(94)90120-1. ISSN 0969-806X.
Sep 21, 2019, 8:40 PM
Citation Linkwww.leginfo.ca.govCalifornia Government Code § 425.2; see "Archived copy". Archived from the original on 28 June 2009. Retrieved 24 December 2009. Cite uses deprecated parameter |deadurl= (help)CS1 maint: archived copy as title (link)
Sep 21, 2019, 8:40 PM
Citation Linkwww.sfgate.comFimrite, Peter (16 July 2010). "Geologists protest bill to remove state rock". SFGate. Retrieved 17 April 2018.
Sep 21, 2019, 8:40 PM
Citation Linkanrcatalog.ucanr.eduFrazell, Julie; Elkins, Rachel; O'Geen, Anthony; Reynolds, Robert; Meyers, James. "Facts about Serpentine Rock and Soil Containing Asbestos in California" (PDF). ANR Catalog. University of California Division of Agriculture and Natural Resources. Retrieved 17 April 2018.
Sep 21, 2019, 8:40 PM
Citation Linkwww.lostcity.washington.edu[1]
Sep 21, 2019, 8:40 PM