Pyrophyllite is a

phyllosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

composed of

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

silicate A silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used ...

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It ...

: Al₂Si₄O₁₀(OH)₂. It occurs in two forms (

habit A habit (or wont, as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously. A 1903 paper in the '' American Journal of Psychology'' defined a "habit, from the standpoint of psychology, ...

s): crystalline folia and compact masses; distinct

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

s are not known. The folia have a pronounced pearly luster, owing to the presence of a perfect cleavage parallel to their surfaces: they are flexible but not elastic, and are usually arranged radially in fan-like or spherical groups. This variety, when heated, exfoliates and swells up to many times its original volume. The color of both varieties is white, pale green, greyish or yellowish; they are very soft (

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...

of 1.0 to 1.5) and are greasy to the touch. The

specific gravity Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

is 2.65–2.85. The two varieties are thus very similar to

talc Talc, or talcum, is a clay mineral composed of hydrated magnesium silicate, with the chemical formula . Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant ...

Occurrence

Pyrophyllite occurs in

phyllite Phyllite ( ) is a type of foliation (geology), foliated metamorphic rock formed from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.Stephen Marshak ''Essentials of Geology'', 3rd ed. I ...

and

schist Schist ( ) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced ''schistosity'' (named for the rock). This means that the rock is composed of mineral grains easily seen with a l ...

ose rocks, often associated with

kyanite Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. It is the high pressure Polymorphism (materials science), polymorph of andalusite and sillimanite, and the presence of kyani ...

, of which it is an alteration product. It also occurs as

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

deposits. Typical associated minerals include: kyanite, andalusite, topaz,

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...

and

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

. Deposits containing well-crystallized material are found in: * Manuels,

Newfoundland and Labrador Newfoundland and Labrador is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region of Labrador, having a total size of . As of 2025 the populatio ...

, Canada, talc-like bright white appearance, high grade, no impurities; 21 million ton deposit. *Russia – pale green foliated masses, very like talc in appearance, are found at Beresovsk near

Yekaterinburg Yekaterinburg (, ; ), alternatively Romanization of Russian, romanized as Ekaterinburg and formerly known as Sverdlovsk ( ; 1924–1991), is a city and the administrative centre of Sverdlovsk Oblast and the Ural Federal District, Russia. The ci ...

in the Urals. * St. Niklas,

Zermatt Zermatt (, ) is a Municipalities of Switzerland, municipality in the district of Visp (district), Visp in the German language, German-speaking section of the canton of Valais in Switzerland. It has a year-round population of about 5,800 and is cl ...

Valais Valais ( , ; ), more formally, the Canton of Valais or Wallis, is one of the cantons of Switzerland, 26 cantons forming the Switzerland, Swiss Confederation. It is composed of thirteen districts and its capital and largest city is Sion, Switzer ...

Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...

* Vaastana,

Kristianstad Kristianstad ( , ) is a Urban areas in Sweden, city and the seat of Kristianstad Municipality, Scania County, Sweden with 41,198 inhabitants in 2023. Since the 1990s, the city has gone from being a garrison town to a developed commercial city, ...

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

* Near Ottrje, Ardennes Mountains,

Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...

* Ibitiara,

Bahia Bahia () is one of the 26 Federative units of Brazil, states of Brazil, located in the Northeast Region, Brazil, Northeast Region of the country. It is the fourth-largest Brazilian state by population (after São Paulo (state), São Paulo, Mina ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

Nagano Prefecture is a Landlocked country, landlocked Prefectures of Japan, prefecture of Japan located in the Chūbu region of Honshu. Nagano Prefecture has a population of 2,007,682 () and has a geographic area of . Nagano Prefecture borders Niigata Prefecture ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

* Near Ogilby, Imperial County at Tres Cerritos, Mariposa County, and the Champion mine, White Mountains,

Mono County, California Mono County ( ) is a county (United States), county located in the east central portion of the U.S. state of California. As of the 2020 United States census, the population was 13,195, making it the fourth-least populous county in California. T ...

, US * Near Quartzsite, La Paz County, Arizona, US * Large deposits at the Deep River region of

North Carolina North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...

, USA *Graves Mountain, Lincoln County, Georgia, US In South Africa, major deposits of pyrophyllite occur within the Ottosdal region, where it is mined for the production of a variety of manufactured goods, and blocks are quarried and marketed as "Wonderstone" for the carving of sculptures.Nel, LT., H. Jacobs, J.T. Allen and G.R. Bozzoli 1937. ''Wonderstone''. Geological Survey of South Africa Bulletin no. 8.

Uses

The compact variety of pyrophyllite is used for slate pencils and tailors' chalk ( French chalk), and is carved by the Chinese into small images and ornaments of various kinds. Other soft compact minerals ( steatite and pinite) used for these Chinese carvings are included with pyrophyllite under the terms agalmatolite and pagodite. Pyrophyllite is easily machineable and has excellent thermal stability, so it is added to clay to reduce thermal expansion when firing, but it has many other industrial uses when combined with other compounds, such as in insecticide and for making bricks. Pyrophyllite is also widely used in high-pressure experiments, both as a

gasket Some seals and gaskets A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression. It is a deformable material that is used to c ...

material and as a pressure-transmitting medium.

References

External links

Mineral galleriesUSGS
{{1911, wstitle=Pyrophyllite, volume=22, pages=695–696 Phyllosilicates Aluminium minerals Triclinic minerals Monoclinic minerals Minerals in space group 2 Minerals in space group 15 Luminescent minerals

Occurrence

Uses

See also

References

External links