Pyrophyllite

Mineral pyrophyllite is a common layer silicate having the chemical composition Al2 [( OH) 2 | Si4O10 ]. It crystallizes polytype in the triclinic crystal system as pyrophyllite -1A and monoclinic crystal system as pyrophyllite - 2M1 and usually develops radial- tufts of needle-like crystals up to about 8 cm size or foliated, granular to massive mineral aggregates of white, gray, greenish or yellow color with white stroke color.

The most translucent to opaque crystals show a greasy to pearly luster, massive aggregates, however, are dull. Pyrophyllite has low Mohs hardness of about 1 to 2, can be so similar to talc already scratched with a fingernail.

Special Features

Pyrophyllite is only sparingly soluble in sulfuric acid, when ignited, it gives off water. Before the blowpipe it scrolls to fan-or worm- shaped, without melting, however. This property also led to its corresponding designation.

Etymology and history

Was first discovered pyrophyllite in the gold deposit of Berezovskoye, in Sverdlovsk Oblast ( Ural ) in Russia and described in 1829 by R. Hermann, of the mineral due to its characteristic behavior before the blowpipe after the Greek words for fire and pyro - πυρο φύλλον phyllon named for leaf.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz pyrophyllite to general ward which was part of " layer silicates ( phyllosilicates ) ", where he formed a distinct group with Ferripyrophyllit, Kegelit, Macaulayit, Minnesotait, talc and Willemseite.

The valid since 2001 and used by the IMA 9th edition of the Strunz'schen Mineral classification assigns the pyrophyllite also in the department of " phyllosilicates ". This division, however, is now more precisely divided according to the structure of the layers, so that the mineral according to its construction in the subdivision of " layer silicates ( phyllosilicates ) with mica sheets, composed of tetrahedral and octahedral nets " can be found, where it sold with Ferripyrophyllit the unnamed group 9.EC.10 forms.

The classification of minerals according to Dana assigns the pyrophyllite in the class of " silicates and Germanates " and there in the department of " layer silicate minerals " one. Here he is with Brinrobertsit, Ferripyrophyllit, Minnesotait, talc, and Willemseite member of the " pyrophyllite - talc group " with the system no. 71.02.01 within the subdivision " layer silicates: layers of six-membered rings with 2:1 layers ".

Modifications and varieties

Agalmatolite is a green variety of pyrophyllite and is used for its jade -like color often confused with it or mistakenly referred to as such.

Education and Locations

Pyrophyllite formed in hydrothermally in corridors and cavities of volcanic rocks and as deposits in schistose metamorphic rocks. Accompanying minerals include kyanite, andalusite, topaz, various mica and quartz.

Worldwide, pyrophyllite so far (as of 2010) are detected at around 500 localities, including, inter alia in Argentina, Australia, Belgium, Bolivia, Brazil, Bulgaria, Chile, China, Germany, Dominican Republic, Ecuador, Fiji, Finland, France, Greece, Indonesia, Israel, Italy, Japan, Canada, Colombia, Madagascar, Morocco, Macedonia, Mexico, Mongolia, Myanmar, Namibia, Norway, Austria, Panama, Papua New Guinea, Peru, Philippines, Portugal, Romania, Russia, Sweden, Switzerland, Serbia, Slovakia, Spain, South Africa, South Korea, Swaziland, Taiwan, Turkey, Uzbekistan, the United Kingdom, the United States of America ( USA) and in Vietnam.

Crystal structure

Pyrophyllite polytype crystallized, that is, it forms of layered combinations of the structural units and with triclinic monoclinic symmetry, referred to as pyrophyllite 1A and pyrophyllite 2M1.

Pyrophyllite -1A crystallizes in the triclinic space group with lattice parameters a = 5.16 Å; b = 8.97 Å; c = 9.35 Å; α = 91.2 °; β = 100.5 ° and γ = 89.6 ° and two formula units per unit cell.

Pyrophyllite - 2M1 crystallizes in the monoclinic space group C2 / c with lattice parameters a = 5.14 Å; b = 8.91 Å; c = 18.60 Å and β = 100.0 °, and four formula units per unit cell.

Use

It is used as a refractory material, insulation material, and as a filler in the paper and plastics industries.

In China, pyrophyllite is called from Zhejiang Province huāyàoshí花 药石and huārǔshí花 乳 石and is a popular material for carving traditional seals.

See also

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