Serpentinite

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Serpentinized
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Maurienne valley, Savoie, French Alps
Sample of serpentinite from the Golden Gate National Recreation Area, California, United States
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 30 cm × 20 cm (11.8 in × 7.9 in).

Serpentinite is a

serpentine group minerals formed by near to complete serpentinization of mafic to ultramafic rocks. Its name originated from the similarity of the texture of the rock to that of the skin of a snake.[1] Serpentinite has been called serpentine or serpentine rock, particularly in older geological texts and in wider cultural settings.[2][3][4][5][6]

Because most of the chemical reactions necessary to synthesize acetyl-CoA, essential to basic biochemical pathways of life, take place during serpentinization, serpentinite thermal vents are a candidate for the environment in which life on Earth originated.

Formation and mineralogy

Serpentinite is formed by near to complete

subduction zones.[9][10]

The final mineral composition of serpentinite is usually dominated by lizardite, chrysotile (two minerals of the serpentine subgroup), and magnetite (Fe3O4). Brucite (Mg(OH)2) and antigorite are less commonly present. Lizardite, chrysotile, and antigorite all have approximately the formula Mg3(Si2O5)(OH)4 or (Mg2+, Fe2+)3Si2O5(OH)4, but differ in minor components and in form.[9] Accessory minerals, present in small quantities, include awaruite, other native metal minerals, and sulfide minerals.[11]

Ophiolite of the Gros Morne National Park, 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 H2 according to the following reaction:

This reaction closely resembles the

oxidation of Fe2+ ions into Fe3+ ions by the protons H+ of water. Two H+
are then reduced into H2.

In the Schikorr reaction, the two

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.[citation needed]

Hydrothermal vents and mud volcanoes

A white carbonate spire in the Lost City hydrothermal field

Deep sea

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 (40 to 75 °C (104 to 167 °F)) that are highly alkaline, high in magnesium, and low in hydrogen sulfide. The vents build up very large chimneys, up to 60 meters (200 ft) 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 200 °C (392 °F).[12] Sepiolite deposits on mid-ocean ridges may have formed through serpentinite-driven hydrothermal activity.[13] However, geologists continue to debate whether serpentinization alone can account for the heat flux from the Lost City field.[12]

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.[14][10] 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.[15][16]

Potential 'cradle of life'

Serpentinite thermal vents are a candidate for the environment in which life on Earth originated.[14] Most of the chemical reactions necessary to synthesize acetyl-CoA, essential to basic biochemical pathways of life, take place during serpentinization.[17] The sulfide-metal clusters that activate many enzymes resemble sulfide minerals formed during serpentinization.[18]

Ecology

Serpentinite ecosystem in the south of New Caledonia

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.[19] 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.[20] 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.[21]

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
]

Occurrences

Notable occurrences of serpentinite are found at

Newfoundland ophiolites, and the Main Ophiolite Belt of New Guinea.[24]

Uses

Drinking cups, examples of serpentinite-turning from Zöblitz in the Erzgebirgskreis
College Hall at University of Pennsylvania

Decorative stone in architecture and art

Serpentine group minerals have a

Larissa, Greece.[26]
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.[27]

By the Inuit

The

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.[28]

  • Magnetic serpentine walrus
    Magnetic serpentine walrus
  • Inuit Elder tending the Qulliq, a ceremonial oil lamp made of serpentinite.
    Inuit Elder tending the Qulliq, a ceremonial oil lamp made of serpentinite.

As an ovenstone

A variety of chlorite talc schist associated with Alpine serpentinite is found in Val d'Anniviers, Switzerland and was used for making "ovenstones" (German: Ofenstein), a carved stone base beneath a cast iron stove.[29]

Neutron shield in nuclear reactors

Serpentinite has a significant amount of

radiation shielding to protect operators from escaping neutrons.[30] Serpentine can also be added as aggregate to special concrete used in nuclear reactor shielding to increase the concrete density (2.6 g/cm3 (0.094 lb/cu in)) and its neutron capture cross section.[31][32]

CO2 sequestration

Because it readily absorbs carbon dioxide, serpentinite may be of use for sequestering atmospheric carbon dioxide.[33] 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.[34] Serpentinite may also be used as a source of magnesium in conjunction with electrolytic cells for CO2 scrubbing.[35]

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."[3] In 2010, a bill was introduced which would have removed serpentine's special status as state rock due to it potentially containing chrysotile asbestos.[36] 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.[37] [needs update]

See also

References

  1. . Retrieved 6 May 2017.
  2. ^ "serpentine". Merriam-Webster.com Dictionary. Merriam-Webster. Retrieved 6 March 2022.
  3. ^ a b California Government Code § 425.2; see "CA Codes (Gov:420-429.8)". Archived from the original on 28 June 2009. Retrieved 24 December 2009.
  4. ^ Oakeshott, G.B. (1968). "Diapiric Structures in Diablo Range, California". AAPG Special Volume M8:Diapirism and Diapirs. 153: 228–243.
  5. .
  6. .
  7. . Retrieved 20 November 2022.
  8. ^ Moody 1976, p. 136.
  9. ^ .
  10. ^ .
  11. .
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  13. .
  14. ^ .
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  16. ^ Marshall, Michael (17 November 2010). "Life is found in deepest layer of Earth's crust". New Scientist. Retrieved 3 December 2021.
  17. PMID 17255002
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  18. . Retrieved 5 September 2021.
  19. ^ "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.
  20. ^ "Serpentinite". Presidio of San Francisco. National Park Service. Retrieved 3 September 2021.
  21. ^ "La flore de Nouvelle-Calédonie – Première partie". Futura-sciences.com. 18 August 2004. Retrieved 30 January 2013.
  22. ^ "6 Serpentine Soil Distributions and Environmental Influences". academic.oup.com. Retrieved 20 November 2022.
  23. .
  24. .
  25. .
  26. ^ Ashurst, John. Dimes, Francis G. Conservation of building and decorative stone. Elsevier Butterworth-Heinemann, 1990, p. 51.
  27. ^ Eva Maria Hoyer: Sächsischer Serpentin: ein Stein und seine Verwendung. Edition Leipzig, Leipzig 1996, pp. 20–22.
  28. ^ Kerr, A.; Squires, G.C. "Serpentinites and associated rock types near Hopedale, Nunatsiavut: Potential for artisanal carving-stone resources" (PDF). Geological Survey Report. 19 (1). Newfoundland and Labrador Department of Natural Resources: 39–57. Retrieved 3 September 2021.
  29. ^ Talcose-schist from Canton Valais. By Thomags Bonney, (Geol. Mag., 1897, N.S., [iv], 4, 110--116) abstract
  30. ^ Lithuanian Energy Institute (28 May 2011). "Design of structures, components, equipments and systems". Ignalina Source Book. Archived from the original on 9 October 2011. Retrieved 28 May 2011.
  31. ^ Aminian, 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. Archived from the original (PDF) on 3 March 2016. Retrieved 28 May 2011.
  32. ISSN 0969-806X
    .
  33. .
  34. .
  35. .
  36. ^ Fimrite, Peter (16 July 2010). "Geologists protest bill to remove state rock". San Francisco Chronicle. Retrieved 17 April 2018.
  37. ^ Frazell, 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.

External links