Argyrodit

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Argyrodit
Argyrodite-170093.jpg
Shiny argyrodite crystal aggregate from Colquechaca, Chayanta, Potosí, Bolivia
General and classification
chemical formula Ag 8 GeS 6
Mineral class
(and possibly department)
Sulfides and sulfosalts
System no. to Strunz
and to Dana
2.BA.70 ( 8th edition : II / B.08)
05/02/06/01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-pyramidal; mm 2
Space group Pna 2 1 (No. 33)Template: room group / 33
Lattice parameters a  = 15.15  Å ; b  = 7.48 Å; c  = 10.59 Å
Formula units Z  = 4
Twinning Pseudospinell Law {111}
Physical Properties
Mohs hardness 2.5 to 3 (VH = 133 to 172)
Density (g / cm 3 ) measured: 6.29; calculated: 6.32
Cleavage Please complete!
Break ; Tenacity uneven to slightly scalloped; brittle
colour steel gray, tapering black
Line color grey black
transparency opaque
shine Metallic luster

Argyrodit is a rarely occurring mineral from the mineral class of " sulfides and sulfosalts ". It crystallizes in the orthorhombic crystal system with the chemical composition Ag 8 GeS 6 .

Argyrodit develops up to 18 cm large crystals with a pseudo-octahedral, -dodecahedral, -cubic habit and combinations of these forms. It can also occur in bunchy or massive mineral aggregates and crusty coatings. When fresh, the opaque crystals are steel-gray in color with a reddish tinge and have a metallic sheen on the surfaces . Over time, the mineral turns black.

Argyrodit forms a mixed crystal row with canfieldite (Ag 8 SnS 6 ) .

Etymology and history

Argyrodit was named after the Greek word άργυρώδης “containing silver” based on its high silver content.

The mineral was first discovered in the Himmelsfürst treasure trove not far from Freiberg and described in 1886 by Albin Weisbach (1833–1901).

In 1886, while analyzing argyrodite, Clemens Winkler discovered the then new element germanium.

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , argyrodite belonged to the mineral class of "sulfides and sulfosalts" and there to the department of "sulfides with the molar ratio of metal: sulfur, selenium, tellurium> 1: 1", where he formed an independent group together with Canfieldit and Putzit .

The 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the International Mineralogical Association (IMA), assigns argyrodite to the class of “sulfides and sulfosalts” and there to the category of “metal sulfides, M: S> 1: 1 (mainly 2: 1) ”. However, this section is further subdivided according to the type of cations involved , so that the mineral can be found according to its composition in the sub-section “with copper (Cu), silver (Ag), gold (Au)” where it is still together forms the unnamed group 2.BA.35 with Canfieldit and Putzit .

The systematics of the minerals according to Dana also assigns the argyrodite to the class of "sulfides and sulfosalts" and there in the department of "sulfide minerals". Here he is the namesake of the " Argyrodit group " with the system no. 02.05.06 and the other member within the subsection "Sulphides - including selenides and tellurides - with the composition A m B n X p , with (m + n): p = 3: 2".

Crystal structure

Argyrodit crystallizes orthorhombically in the space group Pna 2 1 (space group no. 33) with the lattice parameters a  = 15.15  Å ; b  = 7.48 Å and c  = 10.59 Å and 4 formula units per unit cell . Template: room group / 33

properties

Argyrodite specimen that has already tarnished black with some shiny remaining surfaces from Colquechaca, Chayanta, Potosí, Bolivia

Argyrodit consists in its pure form of around 76.5% silver , 6.4% germanium and 17.1% sulfur , but it can also contain admixtures of iron (Fe; 0.7%), tin (Sn; 3.4%) and Contains traces of antimony (Sb).

When heated in a glass tube, which is closed on one side, it produces a shiny black sublimate , whereas in the open glass tube it produces sulphurous acid ; In the soldering tube test on charcoal it finally melts into a ball, which supplies white and lemon-yellow fittings and finally leaves a grain of silver behind.

Education and Locations

Argyrodit settles at relatively low temperatures from hydrothermal solutions mainly in deposits with base metals. It is accompanied by acanthite , aramayoite , chalcopyrite , diaphorite , galena , cassiterite , marcasite and pyrite , polybasite , pyrargyrite , siderite , sphalerite , siderite and stephanite .

As a rare mineral formation, Argyrodite could only be detected at a few sites, whereby so far (as of 2015) around 50 sites are known. In addition to its type locality Himmelsfürst, the "United Field Mine", also located near Brand-Erbisdorf , and the "Beschert Glück Mine" near Zug (Freiberg) in Saxony and the Hornbühl near Waldkirch in Baden-Württemberg are known as other sites in Germany .

Other locations include Jujuy and La Rioja in Argentina, New South Wales in Australia, Oruro and Potosí departments in Bolivia, the provinces of Fujian - and Hubei in China, Auvergne , Limousin and Provence-Alpes-Côte d'Azur in France , County Tipperary in Ireland, Hokkaidō and Honshū in Japan, Souss-Massa-Draâ in Morocco, Guanajuato in Mexico, the North Island of New Zealand, Alba in Romania, the Far East Federal District in Russia, Prešovský kraj in Slovakia, Castile-La Mancha in Spain , Värmland in Sweden, as well as Alaska , Colorado , Nevada and Utah in the USA .

See also

literature

Scientific articles
  • M. Onoda, X.-A. Chen, K. Kato, A. Sato, H. Wada: Structure refinement of Cu 8 GeS 6 using X-ray diffraction data from a multiple-twinned crystal . In: Acta Crystallographica . B55, 1999, p. 721-725 .
  • N. Wang: New data for Ag 8 SnS 6 (canfieldite) and Ag 8 GeS 6 (argyrodite) . In: New Yearbook for Mineralogy. Monthly books . 1978, p. 269-272 .
  • A. Weisbach : Argyrodite, a new silver ore . In: New Yearbook for Mineralogy, Geology and Palaontology . tape 2 , 1886, p. 67–71 ( rruff.info [PDF; 222 kB ]).
In compendia

Web links

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

Individual evidence

  1. a b Webmineral - Argyrodite (English)
  2. a b c 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.  67 .
  3. a b c d Argyrodite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 61 kB )
  4. a b 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.  302 .
  5. ^ A. Weisbach: Argyrodit, a new silver ore. In: New Yearbook for Mineralogy, Geology and Palaontology. Volume 2 (1886), pp. 67–71 ( PDF 222.3 kB )
  6. Mindat - Argyrodite
  7. Mindat - Number of localities for Argyrodit
  8. Find location list for Argyrodit at the Mineralienatlas and at Mindat