Serpentine subgroup

Serpentine subgroup (part of the kaolinite-serpentine group in the category of phyllosilicates)[1] are greenish, brownish, or spotted minerals commonly found in serpentinite. They are used as a source of magnesium and asbestos, and as decorative stone.[5] The name comes from the greenish colour and smooth or scaly appearance from the Latin serpentinus, meaning "serpent rock".[6]

Serpentine
Talk on Serpentine.jpg
General
CategoryPhyllosilicates
Formula
(repeating unit)
X3Si2O5(OH)4, X = Mg2+, Fe2+, Fe3+, Al3+, Ni2+, Mn2+, Zn2+
IMA symbolSrp
Identification
ColorGreen, yellowish-green, blueish-gray (antigorite); green, brown, light yellow to white (lizardite); greyish green to white (chrysotile)
CleavageAlmost perfect
FractureBrittle
Mohs scale hardness3.5–4 (antigorite); 2.5 (lizardite); 2.5–3 (chrysotile)
LusterVitreous, silky, greasy
StreakWhite,greenish-white
Specific gravity2.2-2.9
Diagnostic featuresColor, cleavage
References[1][2][3][4]
Serpentine from Poland

Serpentine subgroup is a set of common rock-forming hydrous magnesium iron phyllosilicate ((Mg,Fe)
3
Si
2
O
5
(OH)
4
) minerals, resulting from the metamorphism of the minerals that are contained in mafic to ultramafic rocks.[7] They may contain minor amounts of other elements including chromium, manganese, cobalt or nickel. In mineralogy and gemology, serpentine may refer to any of the 20 varieties belonging to the serpentine subgroup. Owing to admixture, these varieties are not always easy to individualize, and distinctions are not usually made. There are three important mineral polymorphs of serpentine: antigorite, lizardite and chrysotile.

Serpentine minerals are polymorphous, meaning that they have the same chemical formulae, but the atoms are arranged into different structures, or crystal lattices.[8] Chrysotile, which has a fibrous habit, is one polymorph of serpentine and is one of the more important asbestos minerals. Other polymorphs in the serpentine subgroup may have a platy habit. Antigorite and lizardite are the polymorphs with platy habit.

Many types of serpentine have been used for jewelery and hardstone carving, sometimes under the name 'false jade' or 'Teton jade'.[9][10]

Properties and structureEdit

 
Serpentine chemical structure, single molecule

Most serpentines are opaque to translucent, light (specific gravity between 2.2 and 2.9), soft (hardness 2.5–4), infusible and susceptible to acids.[1] All are microcrystalline and massive in habit, never being found as single crystals. Lustre may be vitreous, silky or greasy. Colours range from white to grey, yellow to green, and brown to black, and are often splotchy or veined. Many are intergrown with other minerals, such as calcite and dolomite.

The basic structural unit of serpentine is a polar layer 0.72 nm thick. A Mg-rich trioctahedral sheet is tightly linked on one side to a single tetrahedral silicate sheet, regardless of the 3–5% larger lateral lattice dimensions of the octahedral sheet.[11] The second level of the structure organized into different serpentine species originates partly to compensate the intra-layer stress due to this dimensional misfit. Good compensation results in a nearly constant layer curvature, with the larger octahedral sheet on the convex side. However, such curvature weakens the H-bonding between the layers. H-bonding tries to maintain flat layers, but this competes with the requirements of misfit compensation. As a result, the layers are locally either curved or flat.[12] Antigorite, lizardite and chrysotile have the same chemical composition, but their different layer of curvatures result in lamellar agglomerated antigorite and lizardite and fibrous chrysotile elongated mineral particles.[13][14]

OccurenceEdit

Serpentine minerals are ubiquitous in many geological systems where hydrothermal alteration of ultramafic rocks is possible, in both terrestrial (oceanic hydrothermalism, subduction zones and transform faulting) and extraterrestrial environments.[15] The process of alteration from mafic minerals to serpentine group minerals is called serpentinization. Serpentine minerals are often formed by the hydration of olivine-rich ultramafic rocks at relatively low temperatures (0 to ~600 °C).[16] The chemical reaction turns olivine into serpentine minerals. They may also have their origins in metamorphic alterations of peridotite and pyroxene. Serpentines may also pseudomorphously replace other magnesium silicates. Incomplete alteration causesthe physical properties of serpentines to vary widely.

Antigorite is the polymorph of serpentine that most commonly forms during metamorphism of wet ultramafic rocks and is stable at the highest temperatures—to over 600 °C (1,112 °F) at depths of 60 km (37 mi) or so. In contrast, lizardite and chrysotile typically form near the Earth's surface and break down at relatively low temperatures, probably well below 400 °C (752 °F). It has been suggested that chrysotile is never stable relative to either of the other two serpentine polymorphs.

Samples of the oceanic crust and uppermost mantle from ocean basins document that ultramafic rocks there commonly contain abundant serpentine. Antigorite contains water in its structure, about 13 percent by weight. Hence, antigorite may play an important role in the transport of water into the earth in subduction zones and in the subsequent release of water to create magmas in island arcs, and some of the water may be carried to yet greater depths.

Occurrence is worldwide, notable localities include New Caledonia, Canada (Quebec), US (northern California, Rhode Island, Connecticut, Massachusetts, Maryland and southern Pennsylvania),[17] Afghanistan, Britain (the Lizard peninsula in Cornwall), Ireland, Greece (Thessaly), China, Russia (Ural Mountains), France, Korea, Austria (Styria and Carinthia), India (Assam, and Manipur), Myanmar (Burma), New Zealand, Norway and Italy.

UsesEdit

 
Dish of serpentine with inlaid gold fish, 1st century BC or AD, with 9th century mounts
 
Budai carved from serpentine, height 8 cm (3 in).

Serpentines find use in industry for several purposes, such as railway ballasts, building materials, and the asbestiform types find use as thermal and electrical insulation (chrysotile asbestos). The asbestos content can be released into the air when serpentine is excavated and if it is used as a road surface, forming a long-term health hazard by breathing. Asbestos from serpentine can also appear at low levels in water supplies through normal weathering processes, but there is as yet no fully proven health hazard associated with use or ingestion, although the EPA states an increased risk of developing benign intestinal polyps can occur.[18] In its natural state, some forms of serpentine react with carbon dioxide and re-release oxygen into the atmosphere.

The more attractive and durable varieties (all of the antigorite) are termed "noble" or "precious" serpentine and are used extensively as gems and in ornamental carvings. The town of Bhera in the historic Punjab province of the Indian subcontinent was known for centuries for finishing a relatively pure form of green serpentine obtained from quarries in Afghanistan into lapidary work, cups, ornamental sword hilts, and dagger handles.[10] This high-grade serpentine ore was known as sang-i-yashm in Persian, or 'false jade' in English, and was used for generations by Indian craftsmen for lapidary work.[10][19] It is easily carved, taking a good polish, and is said to have a pleasingly greasy feel.[20] Less valuable serpentine ores of varying hardness and clarity are also sometimes dyed to imitate jade.[20] Misleading synonyms for this material include "Suzhou jade", "Styrian jade", and "New jade".

New Caledonian serpentine is particularly rich in nickel. The Māori of New Zealand once carved beautiful objects from local serpentine, which they called tangiwai, meaning "tears".

The lapis atracius of the Romans, now known as verde antique, or verde antic, is a serpentinite breccia popular as a decorative facing stone. In classical times it was mined at Casambala, Thessaly, Greece. Serpentinite marbles are also widely used: Green Connemara marble (or 'Irish green marble') from Connemara, Ireland (and many other sources[citation needed]), and red Rosso di Levanto marble from Italy. Use is limited to indoor settings as serpentinites do not weather well.

Potential harmEdit

Soils derived from serpentine are toxic to many plants, because of high levels of nickel, chromium, and cobalt; growth of many plants is also inhibited by low levels of potassium and phosphorus and a low ratio of calcium/magnesium. The flora is generally very distinctive, with specialized, slow-growing species. Areas of serpentine-derived soil will show as strips of shrubland and open, scattered small trees (often conifers) within otherwise forested areas; these areas are called serpentine barrens.

Antigorite varietyEdit

 
Bowenite from Asbestos mine, Thurman Township, Warren County, New York, USA

Lamellated antigorite occurs in tough, pleated masses. It is usually dark green, but may also be yellowish, gray, brown or black. It has a hardness of 3.5–4 and its luster is greasy. The monoclinic crystals show micaceous cleavage and fuse with difficulty. Antigorite is named after its type locality, the Geisspfad serpentinite, Valle Antigorio in the border region of Italy/Switzerland.

BoweniteEdit

Bowenite, a variety of antigorite, is an especially hard serpentine (5.5) of light to dark apple green colour, often mottled with cloudy white patches and darker veining. It is the serpentine most frequently encountered in carving and jewelry. The name 'retinalite' is sometimes applied to yellow bowenite. The New Zealand material is called tangiwai.

Although not an official species, bowenite is the state mineral of Rhode Island, United States: this is also the variety's type locality. A bowenite cabochon featured as part of the "Our Mineral Heritage Brooch", was presented to U.S. First Lady Mrs. Lady Bird Johnson in 1967.

Williamsite is an American local varietal name for antigorite that is oil-green with black crystals of chromite or magnetite often included. Somewhat resembling fine jade, williamsite is cut into cabochons and beads. It is found mainly in Maryland and Pennsylvania.[21]

GymniteEdit

Gymnite is an amorphous form of antigorite.[22] It was originally found in the Bare Hills of Maryland, and is named from the Greek, 'gymnos', meaning "bare" or "naked".

State emblemEdit

In 1965, the California Legislature designated serpentine (the mineral) as “the official State Rock and lithologic emblem.”[23]

GalleryEdit

ReferencesEdit

  1. ^ a b c "Serpentine Subgroup". mindat.org. Retrieved 30 April 2021.
  2. ^ "pyrophyllite | mineral | Britannica". www.britannica.com. Retrieved 2022-11-15.
  3. ^ "Serpentine | NOVA Mineralogy". Retrieved 2022-11-15.
  4. ^ "Serpentine: The mineral Serpentine information and pictures". www.minerals.net. Retrieved 2022-11-15.
  5. ^ Serpentine, American Heritage Dictionary
  6. ^ Rudler, Frederick William (1911). "Serpentine" . In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 24 (11th ed.). Cambridge University Press. pp. 675–677.
  7. ^ "Serpentine definition in the Dictionary of Geology". Retrieved 9 July 2018.
  8. ^ "Serpentine: The mineral Serpentine information and pictures". www.minerals.net. Retrieved 4 April 2018.
  9. ^ National Park Service Archived 2010-09-30 at the Wayback Machine
  10. ^ a b c Hunter, Sir William Wilson and Burn, Sir Richard, The Imperial Gazetteer of India, Vol. 3, Oxford, England: Clarendon Press, Henry Frowde Publishers (1907), p. 242
  11. ^ F. J. Wicks; E. J. W. Whittaker (August 1, 1975). "A reappraisal of the structures of the serpentine minerals". The Canadian Mineralogist. 13 (3): 227–243.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  12. ^ Bernard W. Evans, Keiko Hattori, and Alain Baronnet (April 1, 2013). "Serpentinite: What, Why, Where?". Elements. 9 (2): 99–106.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. ^ D. Hršak, G. Sučik, L. Lazić (2008). "The thermophysical properties of serpentinite". Metalurgija. 47 (1).{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. ^ Shiwei Zhou, Yonggang Wei, Bo Li, Baozhong Ma, Chengyan Wang, Hua Wang (August 5, 2017). "Kinetics study on the dehydroxylation and phase transformation of Mg3Si2O5(OH)4". Journal of Alloys and Compounds. 713: 180–186.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  15. ^ J. F. Mustard, F. Poulet, A. Gendrin, J.-P. Bibring, Y. Lagevin, B. Gondet, N. Mangold, G. Bellucci, And F. Altieri (March 11, 2005). "Olivine and Pyroxene Diversity in the Crust of Mars". Science. 307 (5715): 1594–1597.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  16. ^ Evans, Bernard W. (2004-06-01). "The Serpentinite Multisystem Revisited: Chrysotile Is Metastable". International Geology Review. 46 (6): 479–506. doi:10.2747/0020-6814.46.6.479. ISSN 0020-6814.
  17. ^ "Slate – The Delta Story: A Heritage To Be Preserved". JONES, Jeri L., presented to the Geological Society of America's Northeastern Section. March 2005. Archived from the original on July 14, 2011. Retrieved June 3, 2010.
  18. ^ "National Primary Drinking Water Regulations". 30 November 2015.
  19. ^ Watt, Sir George, The Commercial Products of India, London: John Murray Publishers (1908), p. 561
  20. ^ a b The Stone Age Jewels: Serpentine, retrieved 2 October 2011[permanent dead link]
  21. ^ http://www.cst.cmich.edu/users/dietr1rv/serpentine.htm Archived 2004-06-22 at the Wayback Machine Gemrocks, R. V. Dietrich, 2005
  22. ^ "Gymnite: Gymnite mineral information and data". www.mindat.org. Retrieved 4 April 2018.
  23. ^ California Government Code § 425.2; see "CA Codes (Gov:420-429.8)". Archived from the original on 2009-06-28. Retrieved 2009-12-24.

External linksEdit

  • Mineral description from Mineral galleries
  • Evans, Bernard W. (2004). The Serpentinite Multisystem Revisited: Chrysotile is Metastable. In: International Geology Review, v. 46, pages 479–506
  • Myron G. (2003). Igneous and Metamorphic Petrology, 2nd edition. Blackwell Publishing. ISBN 1-4051-0588-7
  • Kruckeberg, Arthur R. (2002). Geology and Plant Life: the Effects of Landforms and Rock Types on Plants. Seattle: University of Washington Press. ISBN 0-295-98452-X