Arhbarite

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Arhbarite
Arhbarite - El Guanaco Mine (Huanaco), Santa Catalina, Antofagasta, Chile.jpg
Arhbarite (blue) from the El Guanaco Mine, Guanaco (Huanaco), Santa Catalina , Región de Antofagasta , Chile (image size: 4 mm)
General and classification
other names
  • IMA 1981-044
  • IMA 2002-B
chemical formula
  • old formula: Cu 2 [OH | AsO 4 ] · 6H 2 O
  • newly defined formula: Cu 2 Mg [(OH) 3
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.BE.25 ( 8th edition : VII / B.13)
42.06.05.02
Similar minerals Cornetite , McGuinnessite
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triklin-pedial; 1
Space group P 1 (No. 1)Template: room group / 1
Lattice parameters a  = 5.315 (4)  Å ; b  = 5.978 (6) Å; c  = 5.030 (6) Å
α  = 113.58 (6) °; β  = 97.14 (7) °; γ  = 89.30 (8) °
Formula units Z  = 1
Physical Properties
Mohs hardness 5 (VHN 50 = 660 (30) kg / mm 2 )
Density (g / cm 3 ) measured: 3.7 (1)
calculated: 3.96 (type material) to 4.03 (Chilean arhbarite)
Cleavage not observed
colour dark blue
Line color sky blue
transparency translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.720
n γ  = 1.740
Birefringence δ = 0.020
Optical character biaxial
Axis angle 2V = 90 °

Arhbarite is an extremely rare mineral from the mineral class of "phosphates, arsenates and vanadates". It crystallizes in the triclinic crystal system with the chemical composition of Cu 2 Mg [(OH) 3 | AsO 4 ] and is therefore chemically seen a copper - magnesium - arsenate with additional hydroxide .

Arhbarite only develops microscopic, needle-like to tabular crystals up to about 10  micrometers (μm) in length and 2 μm in width, which are usually arranged in spherulitic (spherical) or disk-shaped mineral aggregates of up to 0.5 mm in diameter. The translucent crystals are dark blue in color and have a glass-like sheen on the surfaces. The streak color of the mineral, on the other hand, is rather sky blue.

Etymology and history

Arhbarite was first discovered in the "Arhbar" mine (Arhbar Mine, Aghbar Mine) in the deposits around Bou Azzer (Bou Azer) near the Taznakht oasis in the province of Ouarzazate (Souss-Massa-Draâ region) in southern Morocco and described in 1982 by Karl Schmetzer, Gerd Tremmel and Olaf Medenbach, who named the mineral after its type of locality .

classification

Already in the outdated, but partly still in use 8th edition of the mineral systematics according to Strunz , the arhbarite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the division of "anhydrous phosphates, with foreign anions F, Cl, O, OH", where together with Cornetit , Gilmarit and Klinoklas he formed the unnamed group VII / B.13 .

The 9th edition of Strunz's mineral systematics , which has been valid since 2001 and is used by the IMA, also assigns arhbarite 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, so that the mineral can be classified according to its composition in the subsection "With only medium-sized cations (OH, etc.): RO 4  > 2: 1 "is to be found, where only together with Gilmarit the" Gilmarit group "with the system no. 8.BE.25 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns arhbarite to the class of "phosphates, arsenates and vanadates", although there still according to the outdated chemical composition in the department of "water-containing phosphates etc., with hydroxyl or halogen" a. Here he is together with Strashimirit and Attikait in the " Strashimiritgruppe " with the system no. 42.06.05 within the subsection “Water-containing phosphates etc., with hydroxyl or halogen with (AB) 2 (XO 4 ) Z q × x (H 2 O)”.

Chemism

In their first description, Schmetzer, Tremmel and Medenbach specified Cu 2 [OH | AsO 4 ] · 6H 2 O as the chemical composition . Due to the very small crystal size, however, it was not possible to carry out precise X-ray diffractometry on single crystals at this time . Schmetzer et al. reported an unindexed X-ray powder diffraction pattern ( Debye-Scherrer method ) as the analytical result , which showed no resemblance to other types of mineral or synthetic compounds known at the time.

Only a second discovery of arhbarite in 1998 in the El Guanaco gold mine enabled further investigations on the mineral. The identity of the second find was confirmed by an X-ray diffraction pattern and the semi-quantitative EDX analysis showed good agreement with the data in the original description. The analyzes carried out in 2001 by Werner Krause, Heinz-Jürgen Bernhardt, Herta Effenberger, Uwe Kolitsch and Christian L. Lengauer, however, showed only a very weak absorption of the infrared spectrum in the range 1600 to 1650 cm −1 , which is an indication of a very low absorption or the proportion of molecular water ( water of crystallization ) approaching zero , but was a strong indication of hydroxide ions . Further analyzes also showed that, contrary to the original assumption, the compound also contains magnesium. The Krause et al. The newly defined chemical composition is therefore Cu 2 Mg [(OH) 3 | AsO 4 ]. The redefinition of arhbarite was recognized by the International Mineralogical Association (IMA) in 2002 (internal entry no. 2002-B).

Crystal structure

Arhbarite crystallizes isotypically with Gilmarite in the triclinic crystal system in the space group P 1 (space group no. 1) with the lattice parameters a  = 5.315 (4)  Å ; b  = 5.978 (6) Å; c  = 5.030 (6) Å; α = 113.58 (6) °; β = 97.14 (7) ° and γ = 89.30 (8) ° and one formula unit per unit cell . Template: room group / 1

Education and Locations

Arhbarite (blue-green) with konichalcite (light green) from the El Guanaco Mine, Chile (image width 5 mm)
Dark blue, coarse arhbarite aggregate (below) with light blue, needle-like guanacoite from the El Guanaco mine, Chile (image width 4 mm)

Arhbarit formed in the oxidation zone of polymetallic ore - deposits . Baryte , brochantite , chrysocolla , dolomite , erythrin , guanacoite , hematite , iodine argyite , konichalcite , lollingite , mcguinnessite , olivite , pharmacolite and talc occur as accompanying minerals .

Arhbarite is one of the very rare mineral formations, of which only a few samples exist that have been collected at four known sites so far (as of 2015). Its type locality "Arhbar" is the only place of discovery in Morocco so far.

Otherwise arhbarite could only be discovered in the area of ​​Guanaco (Huanaco) near the town of Santa Catalina in the Chilean region of Antofagasta . The El Guanaco gold mine, from which the material used to redefine the mineral originates and is the namesake for the guanacoite discovered there for the first time, and the nearby Emma Luisa gold mine are particularly well-known.

See also

literature

  • K. Schmetzer, G. Tremmel, O. Medenbach: Arhbarite, Cu 2 [OH | AsO 4 ] · 6H 2 O, a new mineral from Bou-Azzer, Morocco. In: New Yearbook for Mineralogy. Monthly Hefts, 1982, pp. 529-533
  • W. Krause, HJ Bernhardt, H. Effenberger, Uwe Kolitsch, C. Lengauer: Redefinition of arhbarite, Cu 2 Mg (AsO 4 ) (OH) 3 . In: Mineralogical Magazine. Volume 67 (2003), pp. 1099–1107 ( PDF 180.2 kB )

Web links

Commons : Arhbarite  - 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.  497 .
  2. ↑ a b c d e W. Krause, HJ Bernhardt, H. Effenberger, Uwe Kolitsch, C. Lengauer: Redefinition of arhbarite, Cu 2 Mg (AsO 4 ) (OH) 3 . In: Mineralogical Magazine. Volume 67 (2003), pp. 1099–1107 ( PDF 180.2 kB )
  3. ↑ a b W. Krause, HJ Bernhardt, H. Effenberger, Uwe Kolitsch, C. Lengauer: Redefinition of arhbarite, Cu 2 Mg (AsO 4 ) (OH) 3 . In: Mineralogical Magazine. Volume 67 (2003), p. 1101 ( PDF 180.2 kB ; p. 3)
  4. ↑ a b c d Mindat - Arhbarite
  5. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 5th completely revised and supplemented edition. Weise, Munich 2008, ISBN 978-3-921656-70-9 .
  6. ↑ Arhbarite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 63.8 kB )
  7. ^ Joel D. Grice, Giovanni Ferraris: New minerals approved in 2002 and nomenclature modifications approved in 1998-2002 by the Commission on the New Minerals and Mineral Names, International Mineralogical Association. In: The Canadian Mineralogist. Volume 41 (2003), pp. 795–802 ( PDF 42.8 kB ; Arhbarite p. 8)
  8. ↑ Mindat - Number of localities for arhbarite
  9. ↑ Find location list for arhbarite in the Mineralienatlas and Mindat