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 subduction 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 applications soapstone refers to dimension stone that consists of either amphibole-chlorite-carbonate-talc rock, talc-carbonate rock, or simply talc rock and is sold in the form of sawn slabs. "Ground soapstone" sometimes designates the ground waste product of the slab manufacturing. [1]
Petrologically, soapstone is composed predominantly 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. [2] 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, [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.
Soapstone is relatively soft because of its high talc content—talc has 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 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 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. [5] The resulting material, harder than glass, is sometimes called "lava". [6]
Ancient Egyptian scarab signets and amulets were most commonly made from glazed steatite. [7] 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".
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 the Archaic 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 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 have traditionally used soapstone for carvings of both practical objects and art. The qulliq, a type of oil lamp, is carved out of soapstone and used by the Inuit and Dorset 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 in Inuit art. [15]
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.
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 of Tepe Yahya in southeastern Iran 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 the Hoysala Empire, the Western Chalukya Empire and to an extent Vijayanagara Empire. [18]
Even earlier, steatite was used as the substrate for Indus-Harappan seals. [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 the Spring and Autumn period (771–476 BC), soapstone was carved into ceremonial knives. [21] Soapstone was also used to carve Chinese seals.
Soapstone was used as a writing pencil in Myanmar as early as the 11th-century Pagan period. After that, it was still used as a pencil to write on Black Parabaik until the end of the Mandalay period (19th century).
Pipes and decorative carvings of local animals were made out of soapstone by Australian Aboriginal artist Erlikilyika (c. 1865 – c. 1930) in Central Australia. [22]
The Minoan civilization on Crete used soapstone. At the Palace of Knossos, a steatite libation table was found. [23] 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. [24] In Shetland, 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 them Nidaros 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 on wood-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 and magnesite (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 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.
Resistance to heat made steatite suitable for manufacturing gas burner tips, spark plugs, and electrical switchboards. [6]
Steatite ceramics are low-cost biaxial porcelains of nominal composition (MgO)3(SiO2)4. [28] Steatite is used primarily for its dielectric and 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 of mast radiators.
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.
Architectural soapstone is mined in Canada, Brazil, India, and Finland and imported into the United States. [30] 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. [31]
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.
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 including coughing, shortness of breath, cyanosis, crackles, and pulmonary heart disease. Due to the potential presence of tremolite and crystalline silica in the dust, precautions should be taken to avoid occupational diseases such as asbestosis, silicosis, mesothelioma, and lung cancer. [33]
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. [34]
The local names for the soapstone vary: in Vermont, "grit" is used, in Georgia "white-grinding" and "dark-grinding" varieties are distinguished, and California has "soft", "hard", and "blue" talc. [35] Also:
Marble is a metamorphic rock consisting of carbonate minerals (most commonly calcite (CaCO3) or dolomite (CaMg(CO3)2) that have recrystallized under the influence of heat and pressure. It has a crystalline texture, and is typically not foliated (layered), although there are exceptions.
Talc, or talcum, is a clay mineral composed of hydrated magnesium silicate, with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant. It is an ingredient in ceramics, paints, and roofing material. It is a main ingredient in many cosmetics. It occurs as foliated to fibrous masses, and in an exceptionally rare crystal form. It has a perfect basal cleavage and an uneven flat fracture, and it is foliated with a two-dimensional platy form.
The Belcher Islands are an archipelago in the southeast part of Hudson Bay near the centre of the Nastapoka arc. The Belcher Islands are spread out over almost 3,000 km2 (1,200 sq mi). Administratively, they belong to the Qikiqtaaluk Region of Nunavut, Canada. The hamlet of Sanikiluaq is on the north coast of Flaherty Island and is the southernmost in Nunavut. Along with Flaherty Island, the other large islands are Kugong Island, Tukarak Island, and Innetalling Island. Other main islands in the 1,500–island archipelago are Moore Island, Wiegand Island, Split Island, Snape Island and Mavor Island, while island groups include the Sleeper Islands, King George Islands, and Bakers Dozen Islands.
Pyrophyllite is a phyllosilicate mineral composed of aluminium silicate hydroxide: Al2Si4O10(OH)2. It occurs in two forms (habits): crystalline folia and compact masses; distinct crystals are not known.
Stone carving is an activity where pieces of rough natural stone are shaped by the controlled removal of stone. Owing to the permanence of the material, stone work has survived which was created during our prehistory or past time.
The chlorites are the group of phyllosilicate minerals common in low-grade metamorphic rocks and in altered igneous rocks. Greenschist, formed by metamorphism of basalt or other low-silica volcanic rock, typically contains significant amounts of chlorite.
Ultramafic rocks are igneous and meta-igneous rocks with a very low silica content, generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals. The Earth's mantle is composed of ultramafic rocks. Ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks.
Serpentinite is a metamorphic rock composed predominantly of one or more serpentine group minerals formed by near to complete serpentinization of mafic or ultramafic rocks. Its name originated from the similarity of the texture of the rock to that of the skin of a snake. Serpentinite has been called serpentine or serpentine rock, particularly in older geological texts and in wider cultural settings.
Dimension stone is natural stone or rock that has been selected and finished to specific sizes or shapes. Color, texture and pattern, and surface finish of the stone are also normal requirements. Another important selection criterion is durability: the time measure of the ability of dimension stone to endure and to maintain its essential and distinctive characteristics of strength, resistance to decay, and appearance.
A stone sculpture is an object made of stone which has been shaped, usually by carving, or assembled to form a visually interesting three-dimensional shape. Stone is more durable than most alternative materials, making it especially important in architectural sculpture on the outside of buildings.
Inuit art, also known as Eskimo art, refers to artwork produced by Inuit, that is, the people of the Arctic previously known as Eskimos, a term that is now often considered offensive. Historically, their preferred medium was walrus ivory, but since the establishment of southern markets for Inuit art in 1945, prints and figurative works carved in relatively soft stone such as soapstone, serpentinite, or argillite have also become popular.
Asbestos is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere by abrasion and other processes. Inhalation of asbestos fibres can lead to various dangerous lung conditions, including mesothelioma, asbestosis, and lung cancer. As a result of these health effects, asbestos is considered a serious health and safety hazard.
Beer Quarry Caves is a man-made limestone underground complex located about a mile west of the village of Beer, Devon, and the main source in England for Beer stone. The tunnels resulted from 2,000 years of quarrying Beer stone, which was particularly favoured for cathedral and church features such as door and window surrounds because of its colour and workability for carving. Stone from the quarry was used in the construction of several of southern England's ancient cathedrals and a number of other important buildings as well as for many town and village churches, and for some buildings in the United States. Extraction was particularly intense during the Middle Ages, but continued until the 1920s. An adit to another set of workings can be seen from the South West Coast Path east of Branscombe, having been exposed by a landslip in the late 18th century. The quarry is part of the Jurassic Coast, and is a Site of Special Scientific Interest (SSSI).
Hardstone carving, in art history and archaeology, is the artistic carving of semi-precious stones, such as jade, rock crystal, agate, onyx, jasper, serpentinite, or carnelian, and for objects made in this way. Normally the objects are small, and the category overlaps with both jewellery and sculpture. Hardstone carving is sometimes referred to by the Italian term pietre dure; however, pietra dura is the common term used for stone inlay work, which causes some confusion.
Hardstone is a non-scientific term, mostly encountered in the decorative arts or archaeology, that has a similar meaning to semi-precious stones, or gemstones. Very hard building stones, such as granite, are not included in the term in this sense, but only stones which are fairly hard and regarded as attractive – ones which could be used in jewellery. Hardstone carving is the three-dimensional carving for artistic purposes of semi-precious stones such as jade, agate, onyx, rock crystal, sard or carnelian, and a general term for an object made in this way. Two-dimensional inlay techniques for floors, furniture and walls include pietre dure, opus sectile, and medieval Cosmatesque work – these typically inlay hardstone pieces into a background of marble or some other building stone.
Catpund is a quarry site in Shetland, Scotland, where steatite vessels were cut from the rock from prehistory onwards. The quarrying marks are still visible today.
Stone carving in Odisha is the ancient practice of sculpting stone into art and utilitarian objects. It is an ancient practice in the Indian state of Odisha. Stone carving is practiced by artisans mainly in Puri, Bhubaneswar and Lalitgiri in the Cuttack district, though some carvings can be found in Khiching in the Mayurbhanj District. Stone carving is one of the major handcrafts of Odisha. The art form primarily consists of custom carved works, with the Sun Temple of Konark and its intricate sculpture and delicate carvings on the red vivid sandstone exemplifying the practice. Other noteworthy monuments include the Stupas of Udayagiri and Ratnagiri and the temples at Jagannath, Lingaraj, Mukteshwar and as well as other temples in the region.
Qajartalik is a petroglyph site located on the Qajartalik peninsula of Qikertaaluk Island, Nunavut, approximately 40 km southeast of Kangiqsujuaq, Quebec. The site consists of over 150 carvings of faces in soapstone. It was created by the Dorset people, the culture who inhabited the Canadian eastern Arctic and Greenland beginning approximately 2,200 years ago before disappearing approximately 1,000 years ago, and who inhabited the region prior to the Thule Inuit who arrived approximately 800 years ago. It is believed to be the northernmost rock art site in North America and is considered to be one of a kind. The site is currently on Canada's tentative list of sites proposed for inscription on the UNESCO World Heritage List.
In the Kisii region in Kenya, soapstone is mined in the town of Tabaka. It has been at the heart of industry and culture, with its malleability allowing for the carving of a variety of items ranging from common household items to ornaments and other décor items, all of which have found their way into the commercial space, birthing the aforementioned 'industry' around the mining and processing of the ore – largely centered in Tabaka. In its finely milled form, soapstone has been found to have various commercial uses outside carving.
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