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Soapstone (also known as steatite or soaprock) is a metamorphic rock, a talc-schist. It is largely composed of the mineral talc and is thus rich in magnesium. It is produced by dynamothermal metamorphism and metasomatism, which occurs in the areas 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.
Petrologically, soapstone is composed dominantly of talc, with varying amounts of chlorite and amphiboles (typically tremolite, anthophyllite, and magnesiocummingtonite), and trace to minor FeCr-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 dolostones.
Pyrophyllite, a mineral very similar to talc is sometimes called soapstone in the generic sense since its physical characteristics and industrial uses are similar, and because it is also commonly used as a carving material. However this mineral typically does not have such a soapy feel as that from which soapstone derives its name.
Steatite is relatively soft (because of the high talc content, talc being one on Mohs hardness scale), and may feel soapy when touched, hence the name.
The term steatite is sometimes used for soapstone. It is often used as an insulator or housing for electrical components, due to its durability and electrical characteristics and because it can be pressed into complex shapes before firing. Steatite undergoes transformations when heated to temperatures of 1000–1200 °C into enstatite and cristobalite; in the Mohs scale, this corresponds to an increase in hardness from 1 to 5.5–6.5.
Soapstone is used for inlaid designs, sculpture, coasters, and kitchen countertops and sinks. The Inuit often use soapstone for traditional carvings. Some Native American tribes and bands make bowls, cooking slabs, and other objects from soapstone; historically, this was particularly common during the Late Archaic archaeological period.
Vikings hewed soapstone directly from the stone face, shaped it into cooking-pots, and sold these at home and abroad.
Soapstone is sometimes used for fireplace surrounds and woodstoves, because it can absorb and evenly distribute heat while being easy to manufacture. It is also used for counter tops. A weathered or aged appearance will occur naturally over time as the patina is enhanced. Applying mineral oil simply darkens the appearance of the stone; it does not protect it in any way.
Tepe Yahya, an ancient trading city in southeastern Iran, was a centre for the production and distribution of soapstone in the 5th–3rd millennia BC. It was also used in Minoan Crete. At the Palace of Knossos, archaeological recovery has included a magnificent libation table made of steatite. The Yoruba of West Nigeria utilized 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 superstitiously "the staff of Oranmiyan"
Soapstone has been used in India for centuries as a medium for carving. Mining to meet world-wide demand for soapstone is threatening the habitat of India's tigers. The Hoysala Empire temples were made from soapstone.
In Brazil, especially in Minas Gerais, due to the abundance of soapstone mines in that Brazilian state, local artisans still craft objects from that material, including pots and pans, wine glasses, statues, jewel boxes, coasters, vases. 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.
Soapstone is used by welders and fabricators as a marker because, 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 craftsmen as a marking tool because its marks are visible and not permanent. For such purposes, it is often sold in 6-inch-long square or round sticks.
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.
Some Native Americans use soapstone for smoking pipes; numerous examples have been found among artifacts of different cultures and are still in use today. Its lack of heat conduction allows for prolonged smoking without the pipe's heating up uncomfortably.
Soapstone is also a basic stone used to carve Chinese seals.
- 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.
- ↑ "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.
- ↑ Sassaman, Kenneth E., Early Pottery in the Southeast:Tradition and Innovation in Cooking Technology, University of Alabama Press, 1993 ISBN 0-8173-0670-6
- ↑ Else Rosendahl, The Vikings, The Penguin Press, 1987, page 105
- ↑ "Tepe Yahya," Encyclopædia Britannica, 2004. Britannica Concise Encyclopedia. 3 January 2004, Britannica.com
- ↑ C.Michael Hogan (2007) "Knossos Fieldnotes", The Modern Antiquarian
- ↑ Barnett, Antony. "West's love of talc threatens India's tigers", The Guardian, 2003-06-22. URL consultato il 2007-01-09.
- ↑ Belur, Halebid and Sravanabelagola. Retrieved on 2007-01-09.
- ↑ Witthoft, J.G., 1949, "Stone Pipes of the Historic Cherokees", Southern Indian Studies 1(2):43–62.
- ↑ GemRocks: Soapstone
- ↑ Hoysala.in
- Ancient soapstone bowl (The Central States Archaeological Journal)
- Soapstone Native American quarries, Maryland (Geological Society of America)
- Prehistoric soapstone use in northeastern Maryland (Antiquity Journal)
- The Blue Rock Soapstone Quarry, Yancey County, NC (North Carolina Office of State Archaeology)
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