Evansit

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Evansit
Mineraly.sk - evansit.jpg
White Evansite aggregate as a cave filling from Železník in Slovakia
General and classification
chemical formula ~ Al 3 [(OH) 6 | PO 4 ] • 8H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.DF.10 ( 8th edition : VII / D.23)
42.01.02.01
Similar minerals Hyalite
Crystallographic Data
Crystal system amorphous
Physical Properties
Mohs hardness 3 to 4
Density (g / cm 3 ) 2.0
Cleavage no
Break ; Tenacity shell-like, very brittle
colour colorless, milky white, greenish to light blue-green, yellowish
Line color White
transparency transparent to translucent
shine Glass gloss, resin gloss, wax gloss
Crystal optics
Refractive index n  = 1.445 to 1.485
Birefringence δ = about 0.02 possible

Evansite is a rarely occurring minerals from the mineral class of " phosphates , arsenates , and vanadates " with the chemical composition ~ Al 3 [(OH) 6 | PO 4 ] .8H 2 O. One of the few amorphous minerals builds Evansite no defined crystal system to , d. H. its chemical constituents, like glass, arrange themselves randomly during the cooling phase.

Evansite is usually found as transparent to translucent, kidney-shaped to grape-shaped, spherulitic or stalactitic mineral aggregates or crusts of milk-white, greenish to light blue-green or yellowish color with white streak color . Completely colorless Evansite are also known. Smooth, undamaged surfaces have a glass, resin or wax-like sheen .

With a Mohs hardness of around 3 to 4, Evansite is one of the soft to medium-hard minerals and is between the reference minerals calcite (3) and fluorite (4) on the Mohs scale , so it can be easily scratched with a copper coin or a pocket knife.

Etymology and history

Evansite was first discovered at Železník (Vashegy), Sirk in the Revúca district in Slovakia and described in 1864 by David Forbes , who named the mineral after the British metallurgist Brooke Evans (1797–1862). In 1855 he brought the first mineral sample with him from Hungary .

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the evansite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "water-containing phosphates with foreign anions ", where it belonged to Liskeardit , Rosieresit and Sieleckiit formed an independent group.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns Evansite to the class of “phosphates, arsenates and vanadates” and there to the department of “phosphates, etc. without additional anions; without H 2 O “. However, this section is further subdivided according to the size of the cations involved and the molar ratio of the other anions to the phosphate, arsenate or vanadate complex RO 4 , so that the mineral is classified in the sub-section “With only medium-sized cations; (OH etc.): RO 4  > 3: 1 “is to be found, where it forms the unnamed group 8.DF.10 together with Liskeardit and Rosieresit .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Evansite to the class of "phosphates, arsenates and vanadates" and there to the category of "water-containing phosphates, etc., with hydroxyl or halogen ". Here he is the only member of the unnamed group 42.01.02 within the subdivision of " Water-containing phosphates etc., with hydroxyl or halogen with (A) 3 (XO 4 ) Z q × x (H 2 O) ".

Education and Locations

Evansite forms as a phosphate derivative from guano, mostly in the form of crusty cave fillings in graphite-containing deposits , graphitic gneisses and coal layers. Accompanying minerals include variscite , allophane and limonite .

So far (as of 2011) Evansit has been found at around 50 sites. In addition to its type locality Železník (Vashegy), the mineral appeared in Slovakia at Ľubietová and Kociha in the Banská Bystrica region and at Betliar , Dobšiná , Nižná Slaná and Ochtiná in the Košice region .

In Germany, Evansit was only found by chance on a section of the federal highway 224 near Aprath Castle in North Rhine-Westphalia, and the only known location in Austria is a manganese mineralization near the Salzburg municipality of Lend , more precisely near Eschenau in Pinzgau .

Other locations include Australia, Belgium, Bolivia, China, the Democratic Republic of the Congo, France, Japan, Kazakhstan, Madagascar, Portugal, Romania, Russia, Spain, South Africa, the Czech Republic, the United Kingdom (Great Britain) and several federal states of the USA.

See also

literature

Web links

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

Individual evidence

  1. ^ A b Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  506 .
  2. ↑ a b Evansite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 63.5 kB ).
  3. ↑ Find location list for Evansit in the Mineralienatlas and Mindat