Calaverite

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Calaverite
Calaverite-Fluorite-174247.jpg
Callaverite and fluorite from the Doctor Mine (Jackpot Mine), Cripple Creek District, Teller County, Colorado, USA
General and classification
chemical formula AuTe 2
Mineral class
(and possibly department) 		Sulphides and Sulfosalts; Metal: sulfur, selenium, tellurium <1: 1
System no. to Strunz
and to Dana 		2.EA.10 ( 8th edition : II / C.04)
02.12.13.02
Crystallographic Data
Crystal system (monoclinic), aperiodic crystal
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / m (No. 12)Template: room group / 12
Lattice parameters a  = 7.182 to 7.1947  Å ; b  = 4.402 to 4.4146 Å; c  = 5.056 to 5.0703 Å,
β  = 89.99 to 90.038 °
Formula units Z  = 4
Physical Properties
Mohs hardness 2.5 to 3 ( VHN 100 = 197 to 213)
Density (g / cm 3 ) measured: 9.10 to 9.40; calculated: 9.31
Cleavage is missing
Break ; Tenacity uneven to slightly scalloped
colour brass yellow to silver white
Line color greenish to yellowish gray
transparency opaque (opaque)
shine Metallic luster

Calaverite is a rather seldom occurring mineral from the mineral class of "sulfides and sulfosalts" with the chemical composition AuTe 2 and is therefore chemically a gold - ditelluride from the group of substances related to the sulfides , the tellurides.

Calaverite crystallizes in the monoclinic crystal system and develops mostly leafy or short prismatic, longitudinally striped and extensive crystals , but also occurs in the form of granular to massive aggregates . The mineral is always opaque and shows a metallic sheen on the surfaces of the brass-yellow to silver-white crystals . In contrast, its line color is greenish to yellowish-gray.

With a Mohs hardness of 2.5 to 3, calaverite is on the limit of medium-hard minerals. It can no longer be scratched with a fingernail, but it is easier to scratch than the reference mineral calcite (hardness 3) with a copper coin.

Etymology and history

Calaverit was first in the Stanislaus Mine at Carson Hill in Calaveras County ( California ) in the United States found. The first description was made in 1868 by Friedrich August Genth , who took the corresponding mineral samples from I. Adelberg and Louis Beckers and Jas. B. Hodgkin and E. Balbach, Sen. In addition to the new mineral calaverite, Genth found that he named after its type locality , still completely pure Altaite and high gold content Hessite ( Petzite ).

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the calaverite belonged to the mineral class of "sulfides and sulfosalts" and there to the department of "sulfides with M: S <1: 1", where together with Kostovit , Krennerite , Montbrayite , Nagyágit and Sylvanit the "Gold-Silver-Telluride" with the system no. II / C.04 formed.

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. II / D.16-40 . In the “Lapis system”, this also corresponds to the section “Sulphides with metal: S, Se, Te <1: 1”, where calaverite, together with Honeaite , Kostovite, Krennerite and Sylvanite, forms an independent, but unnamed group.

The 9th edition of Strunz's mineral systematics, which has been valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, classifies calaverite in the category of “metal sulfides with M: S ≤ 1: 2”. This is further subdivided according to the exact molar ratio and the predominant metals in the compound, so that the mineral is classified according to its composition in the sub-section “M: S = 1: 2; with Cu, Ag, Au “is to be found, where it is the only member of the unnamed group 2.EA.10 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the calaverite to the class of "sulfides and sulfosalts" and there in the department of "sulfide minerals". Here he is in the " Krennerit group " with the system no. 02.12.13 to be found in the subsection “Sulphides - including selenides and tellurides - with the composition A m B n X p , with (m + n): p = 1: 2”.

Chemism

The idealized, theoretical composition of calaverite consists of 43.56% by weight gold (Au) and 56.44% by weight tellurium (Te). In natural calaverite samples, however, small amounts of silver are often found . In his analyzes of the type material from the Stanislaus mine, Genth himself was able to detect a silver content between 3.0 and 3.5%. Mineral samples from Cripple Creek, Colorado in the USA averaged 0.77 % silver and from Kalgoorlie , Australia 0.60% silver.

Crystal structure

Detail of the crystal lattice structure of calaverite

According to classical mineralogy, calaverite crystallizes in the monoclinic crystal system in the space group C 2 / m (space group no. 12) with the lattice parameters a = 7.182 to 7.1947  Å ; b = 4.402 to 4.4146 Å; c = 5.056 to 5.0703 Å; β = 89.99 to 90.038 ° and four formula units per unit cell . However, in 1931 it was discovered his crystal faces that not all numbers after the law of rational indices of René Just Haüy (see also Miller indices ) can be described. Template: room group / 12

Calverite is one of the aperiodic crystals .

properties

In front of the soldering tube , calaverite colors the flame blue-green and white smoke develops. A grain of gold is formed on charcoal and sublimate made of black tellurium and yellowish-white telluric acid in the glass tube .

Education and Locations

Leafy calaverite in quartz from the Doctor Mine (Jackpot Mine), Cripple Creek District, Teller County , Colorado, USA

Calaverite forms hydrothermally in gold-bearing passages . As Begleitminerale can altaite , Coloradoite , krennerite , Rickardit and other Telluride and arsenopyrite , pyrite , sphalerite , stibnite , Tennantit , tetrahedrite and other sulphides occur.

As a rather seldom occurring mineral formation, calaverite can sometimes be abundant at different sites, but overall it is not very common. Around 400 sites around the world are known to date. In addition to its type locality, the Stanislaus Mine at Carson Hill, the mineral occurred in California in the nearby Melones and Morgan Melones pits and in the French and Wood Mine at Altaville in Calaveras County; at the Darling Mine at Spanish Flat in El Dorado County and the Golden Rule Mine at Jamestown in Tuolumne County .

Cripple Creek is also known due to the significant occurrence of calaverite together with hessite . Calaverite crystals with a diameter of up to one centimeter were also discovered in the Cresson Mine , which is also located in Teller County of Colorado .

Other well-known locations in the USA are Juneau in Alaska, Bisbee in Arizona, as well as some locations in Georgia, Montana, Nevada, New Mexico, North Carolina, South Dakota, Utah, Washington and Wisconsin.

So far, no location for calaverite has been documented in Germany.

The only known site in Austria so far is the Annastollen , a formerly rich gold deposit with uranium enrichments in the mine dumps, about 2.5 km northeast of Mitterberg in the municipality of Mühlbach am Hochkönig in the Salzburg region .

In Switzerland, too, calaverite has so far only been known from one site, namely from the Alpe Formazzolo ( Formazzöö ) with gold-bearing quartz veins near Cevio in the Ticino Valle Maggia .

Other sites with larger deposits are in Australia, Chile, China, Finland, Canada and Russia, among others.

use

Calaverite is an insignificant ore for the extraction of gold.

See also

literature

  • SL Penfield, WE West: Across the Calaverite . In: Journal for Crystallography and Mineralogy . tape 35 , 1902, pp. 430–451 ( rruff.info [PDF; accessed June 21, 2019]).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 454 (first edition: 1891).

Web links

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

Individual evidence

  1. ↑ David Barthelmy: Calaverite Mineral Data. In: webmineral.com. Retrieved June 20, 2019 .
  2. ↑ a b c WJ Schutte, JL de Boer: Valence fluctuations in the incommensurately modulated structure of calaverite AuTe 2 . In: Acta Crystallographica . B44, October 1988, p. 486-494 , doi : 10.1107 / S0108768188007001 (English).
  3. ↑ a b c d Calaverite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 64  kB ; accessed on June 20, 2019]).
  4. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  5. ↑ a b Friedrich August Genth: Contributions to mineralogy - No. VII . In: American Journal of Science and Arts . tape 95 , 1868, pp. 314–316 (English, [1] [PDF; 886 kB ; accessed on June 20, 2019]).
  6. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed June 20, 2019 .
  7. ^ Stefan Schorn and other authors: Aperiodic crystals. In: mineralienatlas.de. Mineral Atlas - Fossil Atlas , accessed June 20, 2019 .
  8. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  454 (first edition: 1891).
  9. ↑ Localities for Calaverite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 21, 2019 .
  10. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 42 .
  11. ^ Stefan Schorn and other authors: Annastollen, Mitterberg, Mühlbach am Hochkönig, St. Johann im Pongau, Salzburg, Austria. In: mineralienatlas.de. Mineral Atlas - Fossil Atlas , accessed June 20, 2019 .
  12. ^ Stefan Schorn and other authors: Alpe Formazzolo (Formazzöö), Cevio, Rovana, Vallemaggia, Ticino, Switzerland. In: mineralienatlas.de. Mineral Atlas - Fossil Atlas , accessed June 20, 2019 .
  13. ↑ Find location list for calaverite in the Mineralienatlas and in Mindat