Pyrophyllite

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Pyrophyllite

Pyrophyllite is a phyllosilicate

Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
mineral

Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
species belonging to the clay

Clay

Clay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired....
family and composed of aluminium

Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
silicate

Silicate

A silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. This definition is broad enough to include species such as hexafluorosilicate , [SiF6]2-, but the silicate species that are encountered most often consist of silicon with oxygen as the ligand...
hydroxide

Hydroxide

In chemistry, hydroxide is the name for the Diatomic molecule anion OH-, consisting of oxygen and hydrogen atoms, usually derived from the Dissociation of a base ....
: AlSi₂O₅OH. It occurs in two more or less distinct varieties, namely, as crystalline folia and as compact masses; distinct crystal

Crystal

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Encyclopedia

Pyrophyllite is a phyllosilicate

Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
mineral

Mineral

Clay

Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
silicate

Silicate

Hydroxide

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions....
s are not known.

The folia have a pronounced pearly lustre, 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 before the blowpipe, exfoliates and swells up to many times its original volume, hence the name pyrophyllite, from the Greek pyros (fire) and phyllos (a leaf), given by R. Hermann in 1829. The color of both varieties is white, pale green, greyish or yellowish; they are very soft (hardness of 1 to 1.5) and are greasy to the touch. The specific gravity

Specific gravity

Specific gravity is defined as the ratio of the density of a given solid or liquid substance to the density of water at a specific temperature and pressure, typically at 4?C and , making it a dimensionless quantity ....
is 2.65 - 2.85. The two varieties are thus very similar to talc

Talc

Talc is a mineral composed of hydrated magnesium silicate with the chemical formula Hydrogen2Magnesium34 or Magnesium3Silicon4Oxygen102....
.

The compact variety of pyrophyllite is used for slate pencils and tailors chalk (French chalk

French chalk

French Chalk is a term used by Max Doerner is his book "The Materials of the Artist" which describes a calcium carbonate used to make traditional gesso grounds....
), 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. In addition, pyrophyllite is widely used in high-pressure presses

Pressure experiment

Pressure experiments are experiments performed at pressures lower or higher than atmospheric pressure, called low-pressure experiments and high-pressure experiments, respectively....
as a pressure-trasmitting medium.

Pyrophyllite occurs in phyllite

Phyllite

Phyllite is a type of Foliation metamorphic rock primarily composed of quartz, sericite mica, and Chlorite group; the rock represents a gradiation in the degree of metamorphism between slate and mica schist....
and schist

Schist

The schists form a group of Erins metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, Chlorite group, talc, hornblende, graphite, and others....
ose rocks, often associated with kyanite

Kyanite

Kyanite, whose name derives from the Greek word kyanos, meaning blue, is a typically blue silicate mineral, commonly found in aluminium-rich metamorphic pegmatites and/or sedimentary rock....
, of which it is an alteration product. Pale green foliated masses, very like talc in appearance, are found at Beresovsk near Yekaterinburg

Yekaterinburg

Yekaterinburg is a major types of inhabited localities in Russia in the central part of Russia, the administrative center of Sverdlovsk Oblast....
in the Ural

Ural Mountains

The Ural Mountains are a mountain range that runs roughly north and south through western Russia. They are usually considered as the natural boundary between Europe and Asia....
s, and at Zermatt

Zermatt

Zermatt is a Municipalities of Switzerland in the district of Visp in the German language-speaking section of the Cantons of Switzerland of Valais in Switzerland....
in Switzerland

Switzerland

Switzerland is a landlocked Swiss Alps country of roughly 7.7 million people in Western Europe with an area of 41,285 km?. Switzerland is a federal republic consisting of 26 states called Cantons of Switzerland....
. The most extensive deposits are in the Deep River

Deep River (North Carolina)

The Deep River is a tributary of the Cape Fear River, approximately 125 miles long, in north central North Carolina in the United States....
region of North Carolina

North Carolina

North Carolina is a U.S. state located on the Atlantic Seaboard in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north....
, where the compact variety is mined, and in South Carolina

South Carolina

South Carolina is a U.S. state in the Southern United States of the United States. It borders Georgia to the south and North Carolina to the north....
and Georgia

Georgia (U.S. state)

Georgia is a U.S. state in the United States and was one of the original Thirteen Colonies that revolted against United Kingdom rule in the American Revolution....
. Major deposits of pyrophyllite occur within region of Ottosdal, South Africa

South Africa

The Republic of South Africa, also known by Official names of South Africa, is a country located at the southern tip of the continent of Africa....
, 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. In Australia, pyrophyllite has been mined at three sites near Pambula on the Sapphire Coast of NSW.

Uses

It is added to clay to reduce thermal expansion when firing but it has many other industry uses when combined with other compounds, such as in insecticide and for making bricks.