Sylvanite

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Sylvanite
Sylvanite (Romania) .jpg
Sylvanit ( writing ore ) from Romania . Exhibited at the Carnegie Museum of Natural History
General and classification
other names
  • Aurum graphicum
  • Goldschmidtit
  • Font
  • Aurotelluride
  • White gold ore
chemical formula
  • AUgT 4
  • (Au, Ag) 2 Te 4
Mineral class
(and possibly department) 		Sulfides and sulfosalts
System no. to Strunz
and to Dana 		2.EA.05 ( 8th edition : II / C.04)
02.12.13.03
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 / c (No. 13)Template: room group / 13
Lattice parameters a  = 8.95  Å ; b  = 4.48 Å; c  = 14.62 Å
β  = 145.3 °
Formula units Z  = 2
Twinning often as contact, lamellar or penetrating twins along {100} or (101)
Physical Properties
Mohs hardness 1.5 to 2 ( VHN 100 = 154 to 172)
Density (g / cm 3 ) measured: 8.16; calculated: 8.161
Cleavage completely after {010}
Break ; Tenacity uneven; brittle
colour steel gray to silver or pewter white, occasionally transitioning to brass yellow
Line color steel gray to silver white
transparency opaque (opaque)
shine Metallic luster

Sylvanit (short Sylvan ), also known as writing ore, is a rather seldom occurring mineral from the mineral class of "sulfides and sulfosalts" with the idealized chemical composition AuAgTe 4 and thus chemically seen a gold - silver - telluride , which chemically with the Sulphides are related.

Sylvanite crystallizes in the monoclinic crystal system and develops steel-gray to silver- or tin-white, occasionally turning brass-yellow crystals with a short prismatic to thick tabular habit and up to one centimeter in size. The surfaces of the completely opaque crystals have a strong metallic luster . Also dendritic lamellar or granular mineral aggregates are known.

Etymology and history

Sylvanite was first found in 1798 in Baia de Arieș , a significant gold-tellurium deposit in Romania before it was closed in 2004. Martin Heinrich Klaproth examined it first and found a ratio of gold to silver to tellurium of 30:10:60. Abraham Gottlob Werner called it Schrifterz, because the arrangement of the crystals is partly reminiscent of drawings. The name sylvanite was given to the mineral by Louis Albert Necker , who named it after Transylvania , the old name of the region in which Baia de Arieș is located.

classification

Already in the outdated 8th edition of the mineral classification according to Strunz , the sylvanite belonged to the mineral class of "sulfides and sulfosalts" and there to the department of "sulfides with M: S <1: 1", where it belongs together with calaverite , Kostovit , Krennerit , Montbrayit and Nagyágit the group of "gold-silver-tellurides" 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.16-20 . In the "Lapis system", this also corresponds to the section "Sulphides with metal: S, Se, Te <1: 1", where sylvanite forms an independent but unnamed group together with calaverite, honeaite , Kostovite and krennerite.

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 sylvanite in the category of “metal sulfides with M: S ≤ 1: 2”. However, 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 ”can be found, where it is the only member of the unnamed group 2.EA.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns sylvanite to the class of "sulphides and sulphosalts" and there in the category of "sulphide 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”.

Crystal structure

Sylvanite crystallizes in the monoclinic crystal system in the space group P 2 / c (space group no. 13) with the lattice parameters a  = 8.95  Å ; b  = 4.48 Å, c  = 14.62 Å and β = 145.3 ° as well as two formula units per unit cell . Template: room group / 13

properties

Sylvanite is one of the few minerals in which gold occurs naturally in the form of a compound. This is because the precious metal gold only forms stable compounds with the rare semi-metal tellurium , while other gold compounds easily decompose to form elemental gold.

Sylvanite melts easily in front of the solder pipe . White smoke appears and gray-metallic globules are initially formed. After a long time, a shiny and malleable pearl is formed.

The mineral deposits gold in nitric acid and silver chloride (chlorine silver ) in aqua regia .

Education and Locations

Sylvanite and purple fluorite

The mineral usually forms at low temperatures under hydrothermal conditions. It is one of the last minerals formed. Sylvanite is associated with gold, calaverite, krennerite, altaite , hessite , petzite , acanthite , pyrite , galena , sphalerite , chalcopyrite , quartz and fluorite .

Sylvanite is found in small amounts in many gold-silver deposits, but larger, economically minable deposits are rare. The sites include Baia de Arieș, Sǎcǎrîmbu and Facebanya in Romania , Glava in Sweden , the southern Urals in Russia , Porcupine in Canada , various mines in the United States, for example in Cripple Creek or Gold Hill , Sonora , Mexico , Kalgoorlie in Australia, Negros Occidental in the Philippines , Guyana and the Fiji Islands .

use

Larger deposits of sylvanite are mined as a raw material for the extraction of gold and tellurium.

literature

  • Martin Heinrich Klaproth: writing ore . In: Contributions to the chemical knowledge of mineral bodies . tape 3 , 1802, pp. 16–20 ( rruff.info [PDF; 319 kB ; accessed on August 16, 2019]).
  • Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Villager Nature ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 41 .

Web links

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

Individual evidence

  1. ↑ a b Martin Heinrich Klaproth: Schrifterz . In: Contributions to the chemical knowledge of mineral bodies . tape 3 , 1802, pp. 16–20 ( rruff.info [PDF; 319 kB ; accessed on August 16, 2019]).
  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.  100 (English).
  3. ↑ a b Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: July 2019. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, July 2019, accessed August 16, 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 c d Sylvanite . 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; 117  kB ; accessed on August 16, 2019]).
  6. ↑ Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 329 .
  7. ↑ Type locality Baia de Arieş (Offenbánya), Alba, Romania. In: mindat.org. Hudson Institute of Mineralogy, accessed August 16, 2019 .
  8. ^ Franz von Kobell: History of Mineralogy . In: History of the Sciences in Germany. Modern times . tape 2 . JG Cottasche Buchhandlung, Munich 1864, p. 563 ( limited preview in Google Book search).
  9. ^ A b William Phillips, Robert Allan: An elementary introduction to mineralogy . 4th edition. Longman, Rees, Orme, Brown, Green, & Longman, London 1837, pp. 341 (English, limited preview in Google Book search).
  10. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed August 16, 2019 .
  11. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1466.
  12. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  453 (first edition: 1891).
  13. ↑ Find location list for sylvanite in the Mineralienatlas and Mindat