Soapstone

Soapstone (also known as steatite or soaprock) is a metamorphic rock, a talc-schist. It is largely composed of the mineral talc and is rich in magnesium. It is produced by dynamothermal metamorphism, which occurs at 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.

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Petrology

  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 stone typically does not have such a soapy feel from which soapstone derives its name.

Physical characteristics and uses

It is relatively soft (because of the high talc content, talc being 1 on Mohs hardness scale), and may feel soapy when touched, hence the name. Soapstone is used for inlaid designs, sculpture, coasters, and kitchen countertops and sinks. Traditional Inuit carvings often use soapstone, and some Native American groups made bowls, cooking slabs, and other objects from soapstone, particularly during the Late Archaic archaeological period.^[1] Due to its chemical stability and resistance to acid, soapstone is the most commonly used material for chemistry lab counter and sink surfaces.^{[citation needed]} Soapstone is sometimes used for fireplace surrounds and woodstoves because it can absorb and evenly distribute heat while being easy to manufacture. This is found in some Alaskan homes. It is also used for griddles and other cookware.

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^[2]

Soapstone has been used in India for centuries as a soft medium for carving, but unfortunately the world wide demand for soapstone is threatening the habitat of India's tigers.^[3] The Hoysala Empire temples were made from soapstone.^[4]

Soapstone markers are used by welders and fabricators as a marker because, due to its resistance to heat, it remains visible when heat is applied.^{[citation needed]} Soapstone is used to create molds for the casting of pewter objects.

Soapstone smoking pipes are found, for example, in Native American Indian artifacts.^{[citation needed]}

Locally quarried soapstone was used as gravemarkers in 19th century northeast Georgia around Dahlonega and Cleveland, as simple field stone and "slot and tab" tombs.

  The term steatite is sometimes used for soapstone. It is also a type of ceramic material made from soapstone with minor additives and heated to vitrify (to change or make into glass or a glassy substance, especially through heat fusion). 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. It was used for beads and seals in ancient civilizations. 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.^[5]

Other names

Kisii stone from Kenya is a type of pyrophyllite used by the Kisii people of the Tabaka Hills in Western Kenya. They use this material to make pots, used to carry fat for massaging into their skin to guard against the elements.

Combarbalite stone, exclusively mined in Combarbala, Chile, is known for its many colors. While they are not visible during mining, they come out after refining.

Palewa and gorara stones are types of Indian soapstone.

A variety of other regional and marketing names for soapstone are used.^[6]

See also

• Ultramafic rock
• Talc carbonate
• Serpentinite
• List of minerals
• See Dina V. for more info

Notes

1. ^ Sassaman, Kenneth E., Early Pottery in the Southeast:Tradition and Innovation in Cooking Technology, University of Alabama Press, 1993 ISBN 0-8173-0670-6
2. ^ "Tepe Yahya." Encyclopædia Britannica. 2004. Britannica Concise Encyclopedia. 3 Jan. 2004 http://concise.britannica.com/ebc/article-9380473/Tepe-Yahya.
3. ^ West's love of talc threatens India's tigers. Retrieved on 2007-01-09.
4. ^ Belur, Halebid and Sravanabelagola. Retrieved on 2007-01-09.
5. ^ 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.
6. ^ http://www.cst.cmich.edu/USERS/DIETR1RV/soapstone.htm