Cornwallit
| Cornwallit | |
|---|---|
 |
|
| General and classification | |
| other names |
Erinit |
| chemical formula | Cu 5 [(OH) 4 | (AsO 4 ) 2 ] |
|
Mineral class (and possibly department) |
Phosphates, arsenates and vanadates |
|
System no. to Strunz and to Dana |
8.BD.05 ( 8th edition : VII / B.11) 04.41.02.02 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Room group (no.) | P 2 1 / c (No. 14) |
| Lattice parameters |
a = 4.59 Å ; b = 5.77 Å; c = 17.34 Å β = 91.8 ° |
| Formula units | Z = 2 |
| Physical Properties | |
| Mohs hardness | 4.5 |
| Density (g / cm 3 ) | measured: 4.17; calculated: 4.64 |
| Cleavage | no |
| Break ; Tenacity | shell-like, uneven in places |
| colour | light green to black green (chip green, grass green) |
| Line color | greenish white |
| transparency | translucent |
| shine | Greasy gloss, matt |
| Crystal optics | |
| Refractive indices |
n α = 1.810 to 1.820 n β = 1.815 to 1.860 n γ = 1.850 to 1.880 |
| Birefringence | δ = 0.040 to 0.060 |
| Optical character | alternating biaxially |
| Axis angle | 2V = 30 to 50 ° (measured); 34 ° (calculated) |
Cornwallite (also Erinite ) is a rather rare mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the monoclinic crystal system with the composition Cu 5 [(OH) 4 | (AsO 4 ) 2 ], so from a chemical point of view it is a copper arsenate with additional hydroxide ions .
Cornwallite is translucent and only develops microscopic crystals that are arranged in radial, kidney or spherical aggregates or form fibrous crusts. Its color varies between light and dark green to black-green, but its line color is more greenish-white. In a spherical aggregate form with smooth surfaces, Cornwallit has a fat-like sheen .
Etymology and history
Cornwallite was first discovered in the English county of Cornwall , more precisely in the Wheal Gorland ore mine near the town of Gwennap , and described in 1846 by Franz Xaver Zippe , who named the mineral after the area where it was found.
The type material of the mineral is kept in the Natural History Museum in London (register no. MI 1985,1754).
classification
In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , cornwallite belonged to the department of "anhydrous phosphates, with foreign anions F, Cl, O, OH", where together with arsenoclasite , cornubite , gatehouseit , ludjibaite , pseudomalachite , Reichenbachit , Reppiait and Turanit formed the unnamed group VII / B.11 .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns Cornwallite to the category of “phosphates etc. with additional anions; without H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the molar ratio of the additional 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 = 2: 1 “is to be found, where the“ pseudomalachite group ”with the system number is only found together with pseudomalachite and Reichenbachite. 8.BD.05 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Cornwallite to the class of "phosphates, arsenates and vanadates" and there to the category of "anhydrous phosphates, etc., with hydroxyl or halogen". Here he is to be found as the only member / together with in the unnamed group 41.04.02 within the sub-section “ Anhydrous phosphates etc., with hydroxyl or halogen with (AB) 5 (XO 4 ) 2 Z q ”.
Crystal structure
Cornwallite crystallizes isotypically with pseudomalachite in the monoclinic crystal system in the space group P 2 1 / c (space group no. 14) with the lattice parameters a = 4.59 Å ; b = 5.77 Å; c = 17.34 Å and β = 91.8 ° and two formula units per unit cell .
properties
When heated in a glass flask, Cornwallite gives off its water of hydration and a grain of copper remains in front of the soldering pipe on carbon, giving off arsenic vapors .
Modifications and varieties
The compound Cu 5 [(OH) 4 | (AsO 4 ) 2 ] is dimorphic and occurs naturally in addition to the monoclinic cornwallite as a triclinic crystallizing cornubite .
Education and Locations
Cornwallite forms secondarily in the oxidation zone of copper deposits . Other copper phosphates or arsenates such as arthurite , austinite , chalcophyllite , cornubite , clinoclase , konichalcite , lavendulan , olivite , strashimirite and tirolite , but also sulfates such as brochantite and spangolite or carbonates such as azurite and malachite can occur as accompanying minerals .
As a rather rare mineral formation, Cornwallite can sometimes be abundant at different sites, but overall it is not very common. So far (as of 2013) around 160 sites are known. In addition to its type locality Wheal Gorland near Gwennap, the mineral occurred in the United Kingdom in several places in the county of Cornwall such as St Hilary and in the counties of Cumbria and Devon in England and at Leadhills in Scotland.
In Germany, Cornwallit has so far been found mainly in the Black Forest , among others near Freudenstadt , Wittichen and Oberwolfach in Baden-Württemberg, but also on the Hartkoppe and Sommerkahl in Bavaria, on Hohenstein in the Hessian community Lautertal , near Bad Lauterberg in the Harz in Lower Saxony , found near Hoffnungsthal (Rösrath) and in several places in Siegerland in North Rhine-Westphalia and Rhineland-Palatinate as well as near Schneeberg and in the mining area Graul in Saxony.
In Austria, Cornwallit has so far only been found on the Silberberg , the Gratlspitze and the Hofer Tratte in the Inntal and on the Graschberg near Thierbach (Wildschönau municipality) in Tyrol.
The only known site in Switzerland so far is the Six-Blanc near Bruson in the Valais municipality of Bagnes .
Other locations include Australia, Brazil, Bulgaria, Chile, China, France, Greece, Ireland, Italy, Japan, Morocco, Mexico, Mongolia, Poland, Portugal, Zimbabwe, Slovakia, Spain, South Africa, the Czech Republic, Hungary and in the United States of America.
See also
literature
- FXM Zippe: About Cornwallite, a new species of the mineral kingdom , In: Treatises of the Royal Bohemian Society of Sciences , Volume 4 (1847), pp. 649-654 ( PDF 1.1 MB )
Web links
- Mineral Atlas: Cornwallite (Wiki)
- Webmineral - Cornwallite
- Database-of-Raman-spectroscopy - Cornwallite
- American-Mineralogist-Crystal-Structure-Database - Cornwallite
Individual evidence
- ↑ a b c d e 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. 448 .
- ↑ a b c Cornwallite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 65.2 kB )
- ↑ a b c Mindat - Cornwallite
- ↑ Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 648 .
- ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke , Stuttgart 1978, ISBN 3-432-82986-8 , pp. 630 (first edition: 1891).
- ↑ FXM Zippe: About Cornwallite, a new species of the mineral kingdom , In: Treatises of the Royal Bohemian Society of Sciences , Volume 4 (1847), p. 652 ( PDF 1.1 MB ; 6)
- ↑ Mindat - Number of localities for Cornwallite
- ↑ Find location list for Cornwallite at the Mineralienatlas and at Mindat