Pyrophyllite

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Pyrophyllite
Pyrophyllite, Quartz - St Niklaus, Matt Valley, Zermatt, Switzerland.jpg
Light green (almost white) pyrophyllite on massive quartz from the Mattertal in Switzerland
General and classification
chemical formula Al 2 [(OH) 2 | Si 4 O 10 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.EC.10 ( 8th edition : VIII / H.09)
71.02.01.01
Crystallographic Data
Crystal system triclinic (pyrophyllite-1A) or monoclinic (pyrophyllite-2M 1 )
Crystal class ; symbol triclinic pinacoidal or monoclinic prismatic
Space group see crystal structure
Lattice parameters see crystal structure
Formula units see crystal structure
Physical Properties
Mohs hardness 1 to 2
Density (g / cm 3 ) measured: 2.65 to 2.90; calculated: 2.81
Cleavage completely after {001}
Break ; Tenacity pliable but not elastic
colour white, gray, greenish, yellow
Line color White
transparency translucent to opaque
shine Grease gloss, pearlescent gloss, matt
Crystal optics
Refractive indices n α  = 1.534 to 1.556
n β  = 1.586 to 1.589
n γ  = 1.596 to 1.601
Birefringence δ = 0.062
Optical character biaxial negative
Axis angle 2V = measured: 53 to 62 °; calculated: 46 to 60 °

The mineral pyrophyllite is a frequently occurring sheet silicate with the chemical composition Al 2 [(OH) 2 | Si 4 O 10 ]. It crystallizes polytype in the triclinic crystal system as pyrophyllite-1A and monoclinic crystal system as pyrophyllite-2M 1 and develops mostly radial tufts of needle-like crystals up to about 8 cm in size or leafy, granular to massive mineral aggregates of white, gray, greenish or yellow color white line color .

The mostly translucent to opaque crystals have a greasy to pearly sheen , while massive aggregates are matt. Pyrophyllite only has a low Mohs hardness of around 1 to 2, so it can be scratched with the fingernail , similar to talc .

Etymology and history

Pyrophyllite was first discovered in the gold deposit of Berezovskoye, in the Sverdlovsk Oblast (Urals) in Russia and described in 1829 by R. Hermann, who used the Greek words πυρο- pyro for fire and φύλλον because of its characteristic behavior in front of the soldering pipe phyllon named for leaf.

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , pyrophyllite belonged to the general division of "phyllosilicates", where it formed an independent group together with ferripyrophyllite , kegelite , macaulayite , minnesotaite , talc and Willemseit .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the IMA, also classifies pyrophyllite in the “phyllosilicates” section. However, this department is now more precisely subdivided according to the structure of the layers, so that the mineral, according to its structure, can be found in the subdivision of "layered silicates (phyllosilicates) with mica sheets, composed of tetrahedral and octahedral nets", where it can only be found together with ferripyrophyllite forms the unnamed group 9.EC.10 .

The systematics of minerals according to Dana also assigns pyrophyllite to the class of "silicates and germanates" and there in the department of "layered silicate minerals". Here, together with brinrobertsite , ferripyrophyllite, minnesotaite, talc and Willemseit, he is a member of the "pyrophyllite talk group" with system no. 71.02.01 within the sub-section " Layered Silicates: Layers of six-membered rings with 2: 1 layers ".

Crystal structure

Pyrophyllite crystallizes polytype , that is, it forms combinations of layer-like structural units with triclinic and monoclinic symmetry, which are referred to as pyrophyllite-1A and pyrophyllite-2M 1 .

Pyrophyllite-1A crystallizes triclinically in the space group C 1 (space group no. 1, position 2) or C 1 (no. 2, position 3) with the lattice parameters a  = 5.16  Å ; b  = 8.97 Å; c  = 9.35 Å; α = 91.2 °; β = 100.5 ° and γ = 89.6 ° as well as 2 formula units per unit cell . Template: room group / 1.2Template: room group / 2.3

Pyrophyllite-2M 1 crystallizes monoclinically in the C 2 / c (No. 15) with the lattice parameters a  = 5.14  Å ; b  = 8.91 Å; c  = 18.60 Å and β = 100.0 ° and 4 formula units per unit cell . Template: room group / 15

properties

Pyrophyllite is in sulfuric acid only sparingly soluble, the glow it gives off water. In front of the soldering tube, it leafs out in the shape of a fan or worm, but without melting. This property also led to its corresponding naming.

Modifications and varieties

Agalmatolite is a green variety of pyrophyllite and is often mistaken for it or incorrectly referred to as such because of its color similar to jade .

Education and Locations

Rutile encrusted with pyrophyllite from the Champion Mine, White Mountain, California

Pyrophyllite forms in hydrothermally in dikes and cavities of volcanic rocks and as a deposit in slate-like, metamorphic rocks . Accompanying minerals include kyanite , andalusite , topaz , various mica and quartz .

So far (as of 2010) pyrophyllite has been found at around 500 sites worldwide, including 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 , Hungary , Uzbekistan , the United Kingdom , the United States of America (USA) and Vietnam .

use

The artisanal use of this material has a long tradition. For example, crosses and medallions with images of saints were made from pyrophyllite in Kiev as early as the 11th century.

Today the mineral is used as a refractory material, insulating material and as a filler in the paper and plastics industries.

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

See also

literature

Web links

Commons : Pyrophyllite  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  662 .
  2. ↑ a b c Pyrophyllite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 73.8 kB )
  3. ↑ a b c d e Pyrophyllite at mindat.org
  4. ↑ History and Perspectives of clay science - Pyrophyllite (Hermann, 1829) ( Memento from May 22, 2013 in the Internet Archive ) (English)
  5. ↑ a b The numbering of this axis position does not correspond to the order of the International Tables for Crystallography , because it is not listed there.
  6. ↑ Find location list for pyrophyllite in the Mineralienatlas and Mindat
  7. ↑ Matsui, Belichenko: Mining, processing and trade in amber from the late Palaeolithic age till the Middle ages in the territory of the present-day Ukraine. In: Trade Routes of Amber. Kaliningrad 2011, pp. 43–54.