Soapstone
Encyclopedia
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
, a talc
Talc
Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg34 or Mg3Si4O102. In loose form, it is the widely-used substance known as talcum powder. It occurs as foliated to fibrous masses, its crystals being so rare as to be almost unknown...
-schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...
. It is largely composed of the mineral talc
Talc
Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg34 or Mg3Si4O102. In loose form, it is the widely-used substance known as talcum powder. It occurs as foliated to fibrous masses, its crystals being so rare as to be almost unknown...
and is thus rich in magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
. It is produced by dynamothermal metamorphism
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
and metasomatism
Metasomatism
Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...
, which occurs in the areas where tectonic plates
Tectonic Plates
Tectonic Plates is a 1992 independent Canadian film directed by Peter Mettler. Mettler also wrote the screenplay based on the play by Robert Lepage. The film stars Marie Gignac, Céline Bonnier and Robert Lepage.-Plot summary:...
are subducted
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
, changing rocks by heat and pressure, with influx of fluids, but without melting. It has been a medium for carving for thousands of years.
Petrology
Petrology
Petrology is the branch of geology that studies rocks, and the conditions in which rocks form....
, soapstone is composed dominantly of talc
Talc
Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg34 or Mg3Si4O102. In loose form, it is the widely-used substance known as talcum powder. It occurs as foliated to fibrous masses, its crystals being so rare as to be almost unknown...
, with varying amounts of chlorite
Chlorite group
The chlorites are a group of phyllosilicate minerals. Chlorites can be described by the following four endmembers based on their chemistry via substitution of the following four elements in the silicate lattice; Mg, Fe, Ni, and Mn....
and amphibole
Amphibole
Amphibole is the name of an important group of generally dark-colored rock-forming inosilicate minerals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures.-Mineralogy:...
s (typically tremolite
Tremolite
Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2Mg5Si8O222. Tremolite forms by metamorphism of sediments rich in dolomite and quartz. Tremolite forms a series with actinolite and ferro-actinolite. Pure magnesium tremolite is creamy white, but the color grades...
, anthophyllite
Anthophyllite
Anthophyllite is an amphibole mineral: 7Si8O222, magnesium iron inosilicate hydroxide. Anthophyllite is polymorphic with cummingtonite. Some forms of anthophyllite are lamellar or fibrous and are used as asbestos...
, and magnesiocummingtonite
Cummingtonite
Cummingtonite is a metamorphic amphibole with the chemical composition 7Si8O222, magnesium iron silicate hydroxide.Monoclinic cummingtonite is compositionally similar and polymorphic with orthorhombic anthophyllite, which is a much more common form of magnesium-rich amphibole, the latter being...
), and trace to minor FeCr-oxide
Oxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
s. It may be schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...
ose or massive. Soapstone is formed by the metamorphism of ultramafic protolith
Protolith
Protolith refers to the precursor lithology of a metamorphic rock.For example, the protolith of a slate is a shale or mudstone. Metamorphic rocks can be derived from any other rock and thus have a wide variety of protoliths. Identifying a protolith is a major aim of metamorphic geology.Sedimentary...
s (e.g. dunite
Dunite
Dunite is an igneous, plutonic rock, of ultramafic composition, with coarse-grained or phaneritic texture. The mineral assemblage is greater than 90% olivine, with minor amounts of other minerals such as pyroxene, chromite and pyrope. Dunite is the olivine-rich end-member of the peridotite group...
or serpentinite
Serpentinite
Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...
) and the metasomatism
Metasomatism
Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...
of siliceous dolostone
Dolostone
Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. In old U.S.G.S. publications it was referred to as magnesian limestone. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification. It is...
s.
Pyrophyllite
Pyrophyllite
Pyrophyllite is a phyllosilicate mineral composed of aluminium silicate hydroxide: Al2Si4O102. It occurs in two more or less distinct varieties, namely, as crystalline folia and as compact masses; distinct crystals are not known....
, 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.
Physical characteristics and uses
Steatite is relatively soft (because of the high talc content, talc being one on Mohs hardness scaleMohs scale of mineral hardness
The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...
), and may feel soapy when touched, hence the name. Soapstone is used for inlaid designs, sculpture, coasters
Beermat
A coaster, drink coaster, beverage coaster, or beermat, is used to rest beverages upon. The main purpose is to protect the surface of a table or any other surface where the user might place their beverage....
, and kitchen countertop
Countertop
Countertop usually refers to a horizontal worksurface in kitchens or other food preparation areas, bathrooms or lavatories, and workrooms in general. It is frequently installed upon and supported by cabinets...
s and sinks. The Inuit
Inuit
The Inuit are a group of culturally similar indigenous peoples inhabiting the Arctic regions of Canada , Denmark , Russia and the United States . Inuit means “the people” in the Inuktitut language...
often used soapstone for traditional carvings. Some Native American
Native Americans in the United States
Native Americans in the United States are the indigenous peoples in North America within the boundaries of the present-day continental United States, parts of Alaska, and the island state of Hawaii. They are composed of numerous, distinct tribes, states, and ethnic groups, many of which survive as...
groups made bowls, cooking slabs, and other objects from soapstone, particularly 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
Stove
A stove is an enclosed heated space. The term is commonly taken to mean an enclosed space in which fuel is burned to provide heating, either to heat the space in which the stove is situated or to heat the stove itself, and items placed on it...
, 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
Tepe Yahya is an archaeological site in Kermān Province, Iran, some 220 km south of Kerman city, 90 km south of Baft city and 90 km south-west of Jiroft.-History:Habitation spans the 6th to 2nd millennia BCE and the 10th to 4th centuries BCE....
, an ancient trading city in southeastern Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...
, was a centre for the production and distribution of soapstone in the 5th–3rd millennia BC. It was also used in Minoan
Minoan civilization
The Minoan civilization was a Bronze Age civilization that arose on the island of Crete and flourished from approximately the 27th century BC to the 15th century BC. It was rediscovered at the beginning of the 20th century through the work of the British archaeologist Arthur Evans...
Crete
Crete
Crete is the largest and most populous of the Greek islands, the fifth largest island in the Mediterranean Sea, and one of the thirteen administrative regions of Greece. It forms a significant part of the economy and cultural heritage of Greece while retaining its own local cultural traits...
. At the Palace of Knossos
Knossos
Knossos , also known as Labyrinth, or Knossos Palace, is the largest Bronze Age archaeological site on Crete and probably the ceremonial and political centre of the Minoan civilization and culture. The palace appears as a maze of workrooms, living spaces, and store rooms close to a central square...
, archaeological recovery has included a magnificent libation
Libation
A libation is a ritual pouring of a liquid as an offering to a god or spirit or in memory of those who have died. It was common in many religions of antiquity and continues to be offered in various cultures today....
table made of steatite.
Soapstone has been used in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
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
Hoysala Empire
The Hoysala Empire was a prominent South Indian Kannadiga empire that ruled most of the modern day state of Karnataka between the 10th and the 14th centuries. The capital of the Hoysalas was initially located at Belur but was later moved to Halebidu....
temples were made from soapstone.
Soapstone is used by welders
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
and fabricators
Fabrication (metal)
Fabrication as an industrial term refers to building metal structures by cutting, bending, and assembling. The cutting part of fabrication is via sawing, shearing, or chiseling ; torching with handheld torches ; and via CNC cutters...
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
Pewter
Pewter is a malleable metal alloy, traditionally 85–99% tin, with the remainder consisting of copper, antimony, bismuth and lead. Copper and antimony act as hardeners while lead is common in the lower grades of pewter, which have a bluish tint. It has a low melting point, around 170–230 °C ,...
or silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
. 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.
Native Americans used soapstone for smoking pipes, and numerous examples have been found among artifacts of different cultures. Its lack of heat conduction allowed for prolonged smoking without the pipe's heating up uncomfortably.
Locally quarried soapstone was used for gravemarkers in 19th century northeast Georgia
Georgia (U.S. state)
Georgia is a state located in the southeastern United States. It was established in 1732, the last of the original Thirteen Colonies. The state is named after King George II of Great Britain. Georgia was the fourth state to ratify the United States Constitution, on January 2, 1788...
around Dahlonega
Dahlonega, Georgia
Dahlonega is a city in Lumpkin County, Georgia, United States, and is its county seat. As of the 2010 census, the city had a population of 5,242....
and Cleveland
Cleveland, Georgia
Cleveland is a city in White County, Georgia, United States. The population was 1,907 at the 2000 census. The city is the county seat of White County....
, as simple field stone and "slot and tab" tombs.
Soapstone is also a basic stone used to carve Chinese seals.
The term steatite is sometimes used for soapstone. It is often used as an insulator
Electrical insulation
thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...
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
Enstatite
Enstatite is the magnesium endmember of the pyroxene silicate mineral series enstatite - ferrosilite . The magnesium rich members of the solid solution series are common rock-forming minerals found in igneous and metamorphic rocks...
and cristobalite
Cristobalite
The mineral cristobalite is a high-temperature polymorph of silica, meaning that it has the same chemical formula, SiO2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the quartz group which also include coesite, tridymite and stishovite...
; in the Mohs scale, this corresponds to an increase in hardness from 1 to 5.5–6.5.
Other names
- Combarbalite stone, exclusively mined in CombarbaláCombarbalaCombarbalá is a Chilean city and commune, located in the Limarí Province, Coquimbo Region. The overall population of the commune is about 14.000 inhabitants, while the population of the city is about 6000 inhabitants...
, ChileChileChile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, 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.
External links
- Ancient soapstone bowl (The Central States Archaeological Journal)
- Soapstone Native American quarries, Maryland (Geological Society of AmericaGeological Society of AmericaThe Geological Society of America is a nonprofit organization dedicated to the advancement of the geosciences. The society was founded in New York in 1888 by Alexander Winchell, John J. Stevenson, Charles H. Hitchcock, John R. Proctor and Edward Orton and has been headquartered at 3300 Penrose...
) - Prehistoric soapstone use in northeastern Maryland (Antiquity Journal)
- The Blue Rock Soapstone Quarry, Yancey County, NC (North Carolina Office of State Archaeology)