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Soapstone (also known assteatite orsoaprock) is atalc-schist, which is a type ofmetamorphic rock. It is composed largely of themagnesium-rich mineraltalc. It is produced by dynamothermalmetamorphism andmetasomatism, 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.
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 applicationssoapstone refers todimension stone that 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]
Petrologically, soapstone is composed predominantly of talc, with varying amounts ofchlorite andamphiboles (typicallytremolite,anthophyllite, andcummingtonite, hence its obsolete name, magnesiocummingtonite), and traces of minor iron-chromiumoxides. It may beschistose ormassive. Soapstone is formed by the metamorphism ofultramaficprotoliths (e.g.dunite orserpentinite) and themetasomatism of siliceousdolomites.
By mass, "pure" steatite is roughly 63%silica, 32%magnesia, and 5% water.[2] It commonly contains minor quantities of other oxides such asCaO orAl2O3.
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 as soapy a feel as soapstone.
Soapstone is relatively soft because of its high proportion of talc, which has a definitional value of 1 on theMohs hardness scale. Softer grades may feel similar tosoap when touched, hence the name. The hardness of soapstone varies due to its varying talc content, 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 aninsulator 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) intoenstatite andcristobalite; 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]
Ancient Egyptianscarab signets and amulets were most commonly made from glazed steatite.[7] TheYoruba people of WestNigeria used soapstone for several statues, most notably atEsie, where archaeologists have uncovered hundreds of male and female statues about half of life size. The Yoruba ofIfe also produced a miniature soapstone obelisk with metal studs called "the staff ofOranmiyan".
Soapstone mining in Tabaka, Kenya occurs 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]
Native Americans have 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 continues 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]
Indigenous peoples of the Arctic have 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 theInuit andDorset peoples.[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, andCleveland as 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]
The ancient trading city ofTepe Yahya in southeasternIran was 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 Empire and 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 inMyanmar as early as the 11th-centuryPagan period. After that, it was still used as a pencil to write on BlackParabaik until the end of the Mandalay period (19th century).
Pipes and decorative carvings of local animals were made out of soapstone byAustralian Aboriginal artistErlikilyika (c. 1865 – c. 1930) inCentral Australia.[22]
TheMinoan civilization onCrete used soapstone. At the Palace ofKnossos, a steatitelibation table was found.[23] Soapstone is relatively abundant in northern Europe. During the Viking Age, soapstone was the primary cooking vessel material in Norway.[24]Vikings hewed soapstone directly from the stone face, shaped it into cooking pots, and sold these at home and abroad.[25] InShetland, there is evidence that these vessels were used for processing marine and dairy fats.[26] Several surviving medieval buildings in northern Europe are constructed with soapstone, amongst themNidaros Cathedral.[4]
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,[27][28] 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.[27][28] 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 forcasting objects from soft metals, such aspewter orsilver. 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 andfabricators 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.
Resistance to heat made steatite suitable for manufacturinggas burner tips,spark plugs, and electrical switchboards.[6]
Steatiteceramics are low-cost biaxialporcelains of nominal composition (MgO)3(SiO2)4.[29] Steatite is used primarily for itsdielectric and thermally-insulating properties in applications such as tile, substrates, washers, bushings, beads, and pigments.[30] It is also used for high-voltage insulators, which have to stand large mechanical loads, such as insulators ofmast radiators.
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.
Architectural soapstone is mined in Canada, Brazil, India, and Finland and imported into the United States.[31] Active North American mines include one south ofQuebec City with products marketed by Canadian Soapstone, the Treasure and Regal mines inBeaverhead County,Montana mined by the Barretts Minerals Company, and another in centralVirginia operated by the Alberene Soapstone Company.
Mining to meet worldwide demand for soapstone is threatening the habitat of India's tigers.[32]
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 introduced around 2007.[33] Most whiskey stones feature a semipolished finish, retaining the soft look of natural soapstone, while others are highly polished.
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 oftremolite and crystallinesilica in the dust, precautions should be taken to avoid occupational diseases such asasbestosis,silicosis,mesothelioma, andlung cancer.[34]
TheOccupational 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. TheNational Institute for Occupational Safety and Health has set arecommended 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 isimmediately dangerous to life and health.[35]
The local names for the soapstone vary: inVermont, "grit" is used, inGeorgia "white-grinding" and "dark-grinding" varieties are distinguished, andCalifornia has "soft", "hard", and "blue" talc.[36] Also:
![Soapstone sculpture on the Hoysala temple at Belur, India[20]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aBelur2_retouched.jpg)
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