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.
A block of talcPetrologically, 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.
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. 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 griddles and other cookware.
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 tiger's habitat. The Hoysala Empire temples were made from soapstone.
Soapstone is also used by welders and fabricators as a marker because, due to its resistance to heat, it remains visible when heat is applied.
Soapstone smoking pipes are also found, for example, among smokers of Cannabis sativa.
Soapstone is also used to create molds for the casting of pewter objects.
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. When steatite is fired at high temperature it produces a much harder variation known as instatite.
Kisii stone from Kenya is a type of soapstone 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 stone is a type of Indian soapstone.
Other regional and marketing names for soapstone are listed by R.V. Dietrich.