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Soapstone

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Samples of soapstone

Soapstone(also known assteatiteorsoaprock) is atalc-schist,which is a type ofmetamorphic rock.It is composed largely of themagnesium-rich mineraltalc.It is produced by dynamothermalmetamorphismandmetasomatism,which occur insubduction zones,changing rocks by heat and pressure, with influx of fluids but without melting. It has been a carving medium for thousands of years.

Terminology

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The definitions of the terms "steatite" and "soapstone" vary with the field of study. In geology, steatite is a rock that is, to a very large extent, composed of talc. The mining industry defines steatite as a high-purity talc rock that is suitable for the manufacturing of, for example,insulators;the lesser grades of the mineral can be called simply "talc rock".Steatite can be used both in lumps (" block steatite "," lava steatite "," lava grade talc "), and in the ground form. While the geologists logically will use" steatite "to designate both forms, in the industry," steatite "without additional qualifications typically means the steatite that is either already ground or to be used in the ground form in the future. If the ground steatite is pressed together into blocks, these are called" synthetic block steatite "," artificial block steatite ", or" artificial lava talc ".[1]

In industrial applicationssoapstonerefers todimension stonethat consists of either amphibole-chlorite-carbonate-talc rock, talc-carbonate rock, or simply talc rock and is sold in the form of sawnslabs."Ground soapstone" sometimes designates the ground waste product of the slab manufacturing.[1]

Petrology

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A block of talc

Petrologically,soapstone is composed predominantly of talc, with varying amounts ofchloriteandamphiboles(typicallytremolite,anthophyllite,andcummingtonite,hence its obsolete name, magnesiocummingtonite), and traces of minor iron-chromiumoxides.It may beschistoseormassive.Soapstone is formed by the metamorphism ofultramaficprotoliths(e.g.duniteorserpentinite) and themetasomatismof siliceousdolomites.

By mass, "pure" steatite is roughly 63.37%silica,31.88%magnesia,and 4.74% water.[2]It commonly contains minor quantities of other oxides such asCaOorAl2O3.

Pyrophyllite,a mineral very similar to talc, is sometimes called soapstone in the generic sense, since its physical characteristics and industrial uses are similar,[3]and because it is also commonly used as a carving material. However, this mineral typically does not have such a soapy feel as soapstone.

Physical characteristics

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Soapstone is relatively soft because of its high talc content—talc has a definitional value of 1 on theMohs hardness scale.Softer grades may feel similar tosoapwhen touched, hence the name. No fixed hardness is given for soapstone because the amount of talc it contains varies widely, from as little as 30% for architectural grades such as those used on countertops, to as much as 80% for carving grades.

Soapstone is easy to carve; it is also durable and heat-resistant and has a high heat storage capacity. It has therefore been used for cooking and heating equipment for thousands of years.[4]

Soapstone is often used as aninsulatorfor housing and electrical components, due to its durability and electrical characteristics and because it can be pressed into complex shapes before firing. Soapstone undergoes transformations when heated to temperatures of 1,000–1,200 °C (1,830–2,190 °F) intoenstatiteandcristobalite;on the Mohs scale, this corresponds to an increase in hardness to 5.5–6.5.[5]The resulting material, harder than glass, is sometimes called "lava".[6]

Historical usage

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Africa

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Ancient Egyptianscarabsignets and amulets were most commonly made from glazed steatite.[7]TheYoruba peopleof WestNigeriaused soapstone for several statues, most notably atEsie,where archaeologists have uncovered hundreds of male and female statues about half of life size. The Yoruba ofIfealso produced a miniature soapstone obelisk with metal studs called "the staff ofOranmiyan".

Soapstone mining in Tabaka, Kenyaoccurs in relatively shallow and accessible quarries in the surrounding areas of Sameta, Nyabigege and Bomware.[8]These were at the time open to all to access provided they had the labor resources to do so. This mostly meant the men did the mining as they were custodian to the community land, meaning ancestral lands in Riamosioma, Itumbe, Nyatike etc.[9]

Americas

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Native Americanshave used soapstone since the Late Archaic period. During theArchaic archaeological period(8000–1000 BC), bowls, cooking slabs, and other objects were made from soapstone.[10]The use of soapstone cooking vessels during this period has been attributed to the rock's thermal qualities; compared to clay or metal containers, soapstone retains heat more effectively.[11]Use of soapstone in native American cultures continue to the modern day. Later, other cultures carved soapstonesmoking pipes,a practice that continues today. The soapstone's low heat conduction allows for prolonged smoking without the pipe heating up uncomfortably.[12]

Mythological figures carved in soapstone by Kayasark, Inuit carver, held in theHonolulu Academy of Arts

Indigenous peoples of theArctichave traditionally used soapstone for carvings of both practical objects and art. Thequlliq,a type of oil lamp, is carved out of soapstone and used by theInuitandDorsetpeoples.[13]The soapstone oil lamps indicate these people had easy access to oils derived from marine mammals.[14]

In the modern period, soapstone is commonly used for carvings inInuit art.[15]

In the United States, locally quarried soapstone was used for gravemarkers in 19th century northeastGeorgia,aroundDahlonega,andClevelandas simple field stone and "slot and tab" tombs.

In Canada, soapstone was quarried in the Arctic regions like the western part of the Ungava Bay and the Appalachian Mountain System from Newfoundland.[16]

Asia

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The 21st-century BCstatue of Iddi-IlumofMari,Syria, is made of soapstone.

The ancient trading city ofTepe Yahyain southeasternIranwas a center for the production and distribution of soapstone in the 5th to 3rd millennia BC.[17]

Soapstone has been used in India as a medium for sculptures since at least the time of theHoysala Empire,theWestern Chalukya Empireand to an extentVijayanagara Empire.[18]

Even earlier, steatite was used as the substrate for Indus-Harappanseals.[19][20]After the intricate carvings of icons and (yet undeciphered) symbols, the seals were heated above 1,000 °C (1,830 °F) for several days to make them hard and durable to make the final seals used for making impressions on clay.

In China, during theSpring and Autumn period(771–476 BC), soapstone was carved into ceremonial knives.[21]Soapstone was also used to carveChinese seals.

Soapstone was used as a writing pencil inMyanmaras early as the 11th-century Pagan period. After that, it was still used as a pencil to write on BlackParabaikuntil the end of the Mandalay period (19th century).

Australia

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Pipes and decorative carvings of local animals were made out of soapstone byAustralian AboriginalartistErlikilyika(c. 1865– c. 1930) inCentral Australia.[22]

Europe

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TheMinoan civilizationonCreteused soapstone. At the Palace ofKnossos,a steatitelibationtable was found.[23]Soapstone is relatively abundant in northern Europe.Vikingshewed soapstone directly from the stone face, shaped it into cooking pots, and sold these at home and abroad.[24]InShetland,there is evidence that these vessels were used for processing marine and dairy fats.[25]Several surviving medieval buildings in northern Europe are constructed with soapstone, amongst themNidaros Cathedral.[4]

Modern usage

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The outer layers of theChrist the Redeemersculpture inRio de Janeiroare made of soapstone.

In modern times, soapstone is most commonly used for architectural applications, such as counter tops, floor tiles, showerbases, and interior surfacing.

Soapstone is sometimes used for construction of fireplace surrounds, cladding onwood-burning stoves,[26][27]and as the preferred material for woodburning masonry heaters because it can absorb, store, and evenly radiate heat due to its high density andmagnesite(MgCO3) content.[26][27]It is also used for countertops and bathroom tiling because of the ease of working the material and its property as the "quiet stone". A weathered or aged appearance occurs naturally over time as the patina is enhanced.

Soapstone can be used to create molds forcastingobjects from soft metals, such aspewterorsilver.The soft stone is easily carved and is not degraded by heating. The slick surface of soapstone allows the finished object to be easily removed.

Weldersandfabricatorsuse soapstone as a marker due to its resistance to heat; it remains visible when heat is applied. It has also been used for many years by seamstresses, carpenters, and other craftspeople as a marking tool, because its marks are visible but not permanent.

Resistance to heat made steatite suitable for manufacturinggas burner tips,spark plugs,and electrical switchboards.[6]

Ceramics

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Steatiteceramicsare low-cost biaxialporcelainsof nominal composition (MgO)3(SiO2)4.[28]Steatite is used primarily for itsdielectricand thermally-insulating properties in applications such as tile, substrates, washers, bushings, beads, and pigments.[29]It is also used for high-voltage insulators, which have to stand large mechanical loads, such as insulators ofmast radiators.

Crafts

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Soapstone continues to be used for carvings and sculptures by artists and indigenous peoples. In Brazil, especially in the state ofMinas Gerais,the abundance of soapstone mines allow local artisans to craft pots, pans, wine glasses, statues, jewel boxes, coasters, and vases from soapstone. These handicrafts are commonly sold in street markets found in cities across the state. Some of the oldest towns, notablyCongonhas,Tiradentes,andOuro Preto,still have some of their streets paved with soapstone from colonial times.

Mining

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Architectural soapstone is mined in Canada, Brazil, India, and Finland and imported into the United States.[30]Active North American mines include one south ofQuebec Citywith products marketed by Canadian Soapstone, the Treasure and Regal mines inBeaverhead County,Montanamined by the Barretts Minerals Company, and another in centralVirginiaoperated by the Alberene Soapstone Company.

Mining to meet worldwide demand for soapstone is threatening the habitat of India's tigers.[31]

Other

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Soapstones can be put in a freezer and later used in place of ice cubes to chill alcoholic beverages without diluting. Sometimes called whiskey stones, these were first introduced around 2007.[32]Most whiskey stones feature a semipolished finish, retaining the soft look of natural soapstone, while others are highly polished.

Safety

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People can be exposed to soapstone dust in the workplace via inhalation and skin or eye contact. Exposure above safe limits can lead to symptoms includingcoughing,shortness of breath,cyanosis,crackles,andpulmonary heart disease.Due to the potential presence oftremoliteand crystallinesilicain the dust, precautions should be taken to avoid occupational diseases such asasbestosis,silicosis,mesothelioma,andlung cancer.[33]

United States

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TheOccupational Safety and Health Administrationhas set the legal limit (permissible exposure limit) for soapstone exposure in the workplace as 20 million particles per cubic foot over an 8-hour workday. TheNational Institute for Occupational Safety and Healthhas set arecommended exposure limitof 6 mg/m3total exposure and 3 mg/m3respiratory exposure over an 8-hour workday. At levels of 3000 mg/m3,soapstone isimmediately dangerous to life and health.[34]

Other names

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The local names for the soapstone vary: inVermont,"grit" is used, inGeorgia"white-grinding" and "dark-grinding" varieties are distinguished, andCaliforniahas "soft", "hard", and "blue" talc.[35]Also:

  • Combarbalite stone, exclusively mined inCombarbalá,Chile, is known for its many colors. While they are not visible during mining, they appear after refining.
  • Palewa and gorara stones are types of Indian soapstone.
  • A variety of other regional and marketing names for soapstone are used.[36]
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See also

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References

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  1. ^abChidester, Engel & Wright 1963,p. 8.
  2. ^Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (1995)."Talc"(PDF).Handbook of Mineralogy.Vol. II (Silica, Silicates). Chantilly, VA: Mineralogical Society of America.ISBN0962209716.
  3. ^Virta, Robert L. (2017).Minerals Yearbook Metals and Minerals 2010.Government Printing Office. p. 75.1.ISBN9788290273908.Retrieved26 November2018.
  4. ^abHansen, Gitte; Storemyr, Per (2017).A Versatile Resource – The Procurement and Use of Soapstone in Norway and The North Atlantic Region. In: Soapstone in the North Quarries, Products and People 7000 BC – AD 1700. UBAS – University of Bergen Archaeological Series 9.Bergen, Norway.ISBN978-82-90273-90-8.{{cite book}}:CS1 maint: location missing publisher (link)
  5. ^"Some Important Aspects of the Harappan Technological Tradition," Bhan KK, Vidale M and Kenoyer JM, inIndian Archaeology in Retrospect/edited by S. Settar and Ravi Korisettar, Manohar Press, New Delhi, 2002.
  6. ^abHall, A. L. (1927)."On the talc deposits near Kaapmuiden, in the Eastern Transvaal".Transactions of the Geological Society of South Africa.30:83.
  7. ^Aldred, Cyril (1971).Jewels of the Pharaohs Egyptian Jewellery of the Dynastic Period.Thames and Hudson. pp. 160–161.ISBN0500231389.
  8. ^Akama, John (2018-08-14)."The Evolution and Resilience of the Gusii Soapstone Industry".Journal of African Cultural Heritage Studies.1(1): 1–17.doi:10.22599/jachs.31.ISSN2513-8243.S2CID169646064.
  9. ^Akama, John (2018-08-14)."The Evolution and Resilience of the Gusii Soapstone Industry".Journal of African Cultural Heritage Studies.1(1): 1.doi:10.22599/jachs.31.ISSN2513-8243.S2CID169646064.
  10. ^Kenneth E. Sassaman (1993-03-30).Early Pottery in the Southeast: Tradition and Innovation in Cooking Technology.University Alabama Press.ISBN978-0-8173-0670-0.
  11. ^Frink, Liam; Glazer, Dashiell; Harry, Karen G. (October 2012)."Canadian Arctic Soapstone Cooking Technology".North American Archaeologist.33(4): 429–449.doi:10.2190/NA.33.4.c.ISSN0197-6931.
  12. ^Witthoft, J.G. (1949). "Stone pipes of the historic Cherokees".Southern Indian Studies.1(2): 43–62.
  13. ^Erwin, John C. (2016)."A Large-Scale Systematic Study of Dorset and Groswater Soapstone Vessel Fragments from Newfoundland and Labrador".Arctic.69:1–8.ISSN0004-0843.
  14. ^"Civilization.ca - Life and Art of an Ancient Arctic People - The Dorset People".historymuseum.ca.Retrieved2024-04-24.
  15. ^Nuttall, Mark (2005-09-23).Encyclopedia of the Arctic.Routledge.ISBN978-1-136-78680-8.
  16. ^O'Driscoll, Cynthia Marie (2003).The application of trace element geochemistry to determine the provenance of soapstone vessels from Dorset Palaeoeskimo sites in western Newfoundland(masters thesis). Memorial University of Newfoundland.
  17. ^"Tepe Yahya,"Encyclopædia Britannica,2004. Britannica Concise Encyclopedia. 3 January 2004,Britannica
  18. ^UGC NET History Paper II Chapter Wise Notebook | Complete Preparation Guide.EduGorilla. 1 September 2022. p. 485.Retrieved26 October2022.
  19. ^Pruthi, R. K. (2004).Indus Civilization.Discovery Publishing House. p. 225.ISBN978-81-7141-865-7.
  20. ^ab"Soapstone sculptures".hoysala.in.2008. Archived fromthe originalon 15 February 2009.Retrieved26 November2018.
  21. ^"Steatite Knife" at the Bath Museum of East Asian Art
  22. ^Kelham, Megg (November 2010)."A museum in Finke: An Aputula Heritage project"(PDF).Territory Stories.pp. 1–97. Archived fromthe original(PDF)on 2019-05-10.Retrieved11 May2019.
  23. ^C.Michael Hogan (2007)"Knossos Fieldnotes",The Modern Antiquarian
  24. ^Else Rosendahl,The Vikings,The Penguin Press, 1987, page 105
  25. ^Steele, Val."Report on the analysis of residues from steatite and ceramic vessels from the site of Belmont, Shetland"(PDF).Shetland Amenity.
  26. ^abWeideman, Paul (2017-11-05)."There's a stove for every taste".The Santa Fe New Mexican.Retrieved2017-12-14.
  27. ^abDamrosch, Barbara (2017-01-19)."The enduring appeal of wood stoves".The Washington Post.Retrieved2017-12-14.
  28. ^"Royalty Minerals".royaltyminerals.in.Retrieved26 November2018.
  29. ^"Superior Technical Ceramics".Retrieved26 November2018.
  30. ^"Soapstone gives countertops, tiles a look that's both new and old".The Washington Post.2013-05-30.Retrieved2014-01-11.
  31. ^Barnett, Antony (2003-06-22)."West's love of talc threatens India's tigers".The Guardian.London.Retrieved2007-01-09.
  32. ^"Interview with the Inventor of Whisky Stones, Andrew Hellman".Whisky Stones.Retrieved2021-06-08.
  33. ^Proctor, Nick H.; Hughes, James P.; Hathaway, Gloria J. (2004).Proctor and Hughes' Chemical hazards of the workplace(5th ed.). Hoboken, NJ: Wiley-Interscience.ISBN978-0-471-26883-3.
  34. ^"CDC - NIOSH Pocket Guide to Chemical Hazards - Soapstone (containing less than 1% quartz)".cdc.gov.Retrieved2015-11-21.
  35. ^Chidester, Engel & Wright 1963,pp. 8–9.
  36. ^"CST Personal Home Pages".cst.cmich.edu.Retrieved26 November2018.

Sources

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Further reading

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