Steatite
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Steatite
Several colored samples of soapstone.

Soapstone (also known as steatite or soaprock) is a talc-schist, which is a type of metamorphic rock. It is composed largely of the magnesium rich mineral talc. It is produced by dynamothermal metamorphism and metasomatism, which occur in the zones where tectonic plates are subducted, changing rocks by heat and pressure, with influx of fluids, but without melting. It has been a medium for carving for thousands of years.[]

Petrology

A block of talc

Petrologically, soapstone is composed dominantly of talc, with varying amounts of chlorite and amphiboles (typically tremolite, anthophyllite, and cummingtonite, hence its obsolete name, magnesiocummingtonite), and traces of minor iron-chromium oxides. It may be schistose or massive. Soapstone is formed by the metamorphism of ultramafic protoliths (e.g. dunite or serpentinite) and the metasomatism of siliceous dolomites.

By mass, "pure" steatite is roughly 63.37% silica, 31.88% magnesia, and 4.74% water.[1] It commonly contains minor quantities of other oxides such as CaO or Al2O3.

Pyrophyllite, a mineral very similar to talc, is sometimes called soapstone in the generic sense, since its physical characteristics and industrial uses are similar,[2] 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

Soapstone is relatively soft because of its high talc content, talc having a definitional value of 1 on the Mohs hardness scale. Softer grades may feel similar to soap when 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, heat-resistant and has a high heat storage capacity. It has therefore been used for cooking and heating equipment for thousands of years.[3]

Soapstone is often used as an insulator for 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) into enstatite and cristobalite; on the Mohs scale, this corresponds to an increase in hardness to 5.5-6.5.[4]

Uses

Historical

Soapstone has been used widely throughout history, by many cultures.

Africa

Ancient Egyptian scarab signets and amulets were most commonly made from glazed steatite.[5] The Yoruba people of West Nigeria used soapstone for several statues, most notably at Esie, where archaeologists have uncovered hundreds of male and female statues about half of life size. The Yoruba of Ife also produced a miniature soapstone obelisk with metal studs called "the staff of Oranmiyan".

West Asia

The 21st-century BC statue of Iddi-Ilum of Mari is made of soapstone.

The ancient trading city of Tepe Yahya in southeastern Iran was a center for the production and distribution of soapstone in the 5th to 3rd millennia BC.[6]

Europe

The Minoan civilization on Crete used soapstone. At the Palace of Knossos, a steatite libation table was found.[7] Soapstone is relatively abundant in northern Europe. Vikings hewed soapstone directly from the stone face, shaped it into cooking pots, and sold these at home and abroad.[8] In Shetland, there is evidence these vessels were used for processing marine and dairy fats.[9] Several surviving medieval buildings in northern Europe are constructed with soapstone, amongst them Nidaros Cathedral.[3]

South Asia

Soapstone has been used in India for millennia as a medium for carving, perhaps most famously in the so-called Priest-King sculpture) from the Bronze Age Indus Valley Civilization site of Mohenjo-Daro.

East Asia

During the Spring and Autumn Period (771-476 BC), soapstone was carved into ceremonial knives.[10] Soapstone was also used to carve Chinese seals.

Americas

Native Americans have used soapstone since the Late Archaic Period. During the Archaic archaeological period (8000-1000 BC), bowls, cooking slabs, and other objects were made from soapstone.[11] Use of soapstone in native American cultures continue to the modern day. Later, other cultures carved soapstone smoking pipes, a practice that continues today. The soapstone's low heat conduction allows for prolonged smoking without the pipe heating up uncomfortably.[12]

Indigenous peoples of the arctic made use of soapstone in carvings. The qulliq, a type of oil lamp, is carved out of soapstone and used by the Inuit, Chukchi, and Yupik peoples. This kind of lamp was the single most important article of furniture for the Inuit peoples in their dwellings.

In the United States, locally quarried soapstone was used for gravemarkers in 19th century northeast Georgia, around Dahlonega, and Cleveland as simple field stone and "slot and tab" tombs. Small blocks of soapstone (8" x 10" x 1") were also heated on the cookstove or near the fire and used to warm cold bedclothes or to keep hands and feet cozy while sleighing.

Australia

Pipes and decorative carvings of local animals were made out of soapstone by Australian Aboriginal artist Erlikilyika (c.1865-c.1930) in Central Australia.[13]

Modern

The outer layers of the Christ the Redeemer sculpture in Rio de Janeiro are 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 on wood-burning stoves,[14][15] and as the preferred material for woodburning masonry heaters because it can absorb, store, and evenly radiate heat due to its high density and magnesite (MgCO3) content.[14][15] 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 for casting objects from soft metals, such as pewter or silver. 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.

Welders and fabricators use 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.

Ceramics

Steatite ceramics are low-cost biaxial porcelains of nominal composition (MgO)3(SiO2)4.[16] Steatite is used primarily for its dielectric and thermal insulating properties in applications such as tile, substrates, washers, bushings, beads, and pigments.[17] It is also used for high-voltage insulators, which have to stand large mechanical loads, e.g. insulators of mast radiators.

Crafts

Soapstone continues to be used for carvings and sculptures by artists and indigenous peoples. In Brazil, especially in the state of Minas 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, notably Congonhas, Tiradentes, and Ouro Preto, still have some of their streets paved with soapstone from colonial times.

Others

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.[18] Most whiskey stones feature a semipolished finish, retaining the soft look of natural soapstone, while others are highly polished.

Mining

Architectural soapstone is mined in Canada, Brazil, India, and Finland and imported into the United States.[19] Active North American mines include one south of Quebec City with products marketed by Canadian Soapstone, the Treasure and Regal mines in Beaverhead County, Montana mined by the Barretts Minerals Company, and another in Central Virginia operated by the Alberene Soapstone Company.

Mining to meet worldwide demand for soapstone is threatening the habitat of India's tigers.[20]

Safety

People can be exposed to soapstone in the workplace via inhalation and skin or eye contact. Exposure above safe limits can lead to symptoms including coughing, shortness of breath, cyanosis, crackles, and pulmonary heart disease.

United States

The Occupational Safety and Health Administration has 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. The National Institute for Occupational Safety and Health has set a recommended exposure limit of 6 mg/m3 total exposure and 3 mg/m3 respiratory exposure over an 8-hour workday. At levels of 3000 mg/m3, soapstone is immediately dangerous to life and health.[21]

Other names

  • Combarbalite stone, exclusively mined in Combarbalá, 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.[22]

Gallery

See also

References

  1. ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (1995). "Talc" (PDF). Handbook of Mineralogy. II (Silica, Silicates). Chantilly, VA: Mineralogical Society of America. ISBN 0962209716.
  2. ^ Virta, Robert L. Minerals Yearbook Metals and Minerals 2010. Government Printing Office. p. 75.1. ISBN 9788290273908. Retrieved 2018.
  3. ^ a b Hansen, 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. ISBN 978-82-90273-90-8.
  4. ^ "Some Important Aspects of the Harappan Technological Tradition," Bhan KK, Vidale M and Kenoyer JM, in Indian Archaeology in Retrospect/edited by S. Settar and Ravi Korisettar, Manohar Press, New Delhi, 2002.
  5. ^ Aldred, Cyril (1971). Jewels of the Pharaohs Egyptian Jewellery of the Dynastic Period. Thames and Hudson. pp. 160-161. ISBN 0500231389.
  6. ^ "Tepe Yahya," Encyclopædia Britannica, 2004. Britannica Concise Encyclopedia. 3 January 2004, Britannica.com
  7. ^ C.Michael Hogan (2007) "Knossos Fieldnotes", The Modern Antiquarian
  8. ^ Else Rosendahl, The Vikings, The Penguin Press, 1987, page 105
  9. ^ Steele, Val. "Report on the analysis of residues from steatite and ceramic vessels from the site of Belmont, Shetland" (PDF). Shetland Amenity.
  10. ^ "Steatite Knife" at the Bath Museum of East Asian Art
  11. ^ Kenneth E. Sassaman (1993-03-30). Early Pottery in the Southeast: Tradition and Innovation in Cooking Technology. University Alabama Press. ISBN 978-0-8173-0670-0.
  12. ^ Witthoft, J.G. (1949). "Stone pipes of the historic Cherokees". Southern Indian Studies. 1 (2): 43-62.
  13. ^ Kelham, Megg (November 2010). "A museum in Finke: An Aputula Heritage project" (PDF). See Territory Stories for details of document: 1-97. Retrieved 2019. Cite journal requires |journal= (help)
  14. ^ a b Weideman, Paul (2017-11-05). "There's a stove for every taste". The Santa Fe New Mexican. Retrieved .
  15. ^ a b Damrosch, Barbara (2017-01-19). "The enduring appeal of wood stoves". The Washington Post. Retrieved .
  16. ^ "Royalty Minerals". royaltyminerals.in. Retrieved 2018.
  17. ^ "Superior Technical Ceramics". Retrieved 2018.
  18. ^ "Interview with the Inventor of Whisky Stones, Andrew Hellman". Whisky Stones. Retrieved .
  19. ^ "Soapstone gives countertops, tiles a look that's both new and old". The Washington Post. 2013-05-30. Retrieved .
  20. ^ Barnett, Antony (2003-06-22). "West's love of talc threatens India's tigers". The Guardian. London. Retrieved .
  21. ^ "CDC - NIOSH Pocket Guide to Chemical Hazards - Soapstone (containing less than 1% quartz)". www.cdc.gov. Retrieved .
  22. ^ "CST Personal Home Pages". cst.cmich.edu. Retrieved 2018.
  23. ^ "Soapstone sculptures". hoysala.in. 2008. Archived from the original on 15 February 2009. Retrieved 2018.

Further reading

External links


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Steatite
 



 



 
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