Geocronite

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Geocronite
Geocronite-616592.jpg
Coarse aggregate of light gray, shiny metallic geocronite from the Young America Mine, Bossburg, Northport District, Stevens County (Washington) , USA (size: 47 mm × 42 mm × 15 mm)
General and classification
other names
  • School quote
  • Kilbrickenit
chemical formula
  • Pb 14 (Sb, As) 6 S 23
  • Pb 14 [S 5 | (AsS 3 ) 2 ((Sb, As) S 3 ) 4 ]
Mineral class
(and possibly department) 		Sulfides and sulfosalts
System no. to Strunz
and to Dana 		2.JB.30a ( 8th edition : II / E.15)
03.03.01.02
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / m (No. 11)Template: room group / 11
Lattice parameters a  = 8.96  Å ; b  = 31.93 Å; c  = 8.50 Å
β  = 118.0 °
Formula units Z  = 2
Frequent crystal faces {001}
Twinning often lamellar according to {101} or {001}
Physical Properties
Mohs hardness 2.5
Density (g / cm 3 ) measured: 6.46; calculated: 6.44
Cleavage indistinct, uneven
Break ; Tenacity clamshell; mild
colour light lead gray to light gray, tapering to black
Line color light lead gray to gray blue
transparency opaque
shine Metallic luster

Geokronit is a relatively rarely occurring minerals from the mineral class of "sulphides and thio" with the chemical composition Pb 14 (Sb, As) 6 S 23 , is due to its crystal structure to the lead - thio-salts with antimony . The elements antimony and arsenic indicated in the round brackets can represent each other in the formula ( substitution , diadochy), but are always in the same proportion to the other components of the mineral.

Geocronite is opaque and crystallizes in the monoclinic crystal system , but rarely develops well-formed, tabular crystals and twins . However, these can be up to 8 cm in size. It is mostly found in the form of granular, massive or earthy mineral aggregates from light gray to lead gray, metallic shimmering color. In the air, Geokronit can turn black over time.

With its relative Jordanite (Pb 14 (As, Sb) 6 S 23 ), Geokronite forms a complete mixed crystal series.

Etymology and history

Geokronite was first discovered in the silver mines of Sala in the Swedish province of Västmanland County and described in 1839 by chemist and mineralogist Lars Fredrik Svanberg (1805–1878).

He named the mineral after the Greek terms γή [ Gaia ] (also Gea or Gäa ) for earth and κρόνος [ Kronos ] (Roman Saturn ). The parts of the name are an allusion to the composition of the mineral with the main components lead and antimony , which are assigned to Saturn and Earth as planetary metals .

classification

In the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the geokronite belonged to the mineral class of "sulfides and sulfosalts" and there to the department of "sulfosalts (S: As, Sb, Bi = x)", where it belongs together Gratonite , Jordanite , Lengenbachite , Meneghinite and Tsugaruit the group of "lead sulfosalts with As / Sb (x = 3.8-3.1)" with the system no. II / E.15 formed.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns Geokronite to the department of “sulfosalts with PbS as a model”. This is further subdivided according to the crystal structure , so that the mineral can be found according to its composition and structure in the sub-section " Galena derivatives with lead (Pb)", where it is only together with jordanite the "jordanite group" with the system -No. 2.JB.30a forms.

Also the systematics of minerals according to Dana , which is mainly used in the English-speaking area , assigns geocronite to the class of "sulfides and sulfosalts" and there in the department of "sulfosalts". Here he is also together with Jordanit in the unnamed group 03.03.01 within the subsection " Sulphosalts with the ratio 3 <z / y <4 and the composition (A + ) i (A 2+ ) j [B y C z ], A = metals, B = semi-metals, C = non-metals ”.

Crystal structure

Geocronite crystallizes isotypically with jordanite in the monoclinic crystal system in the space group P 2 1 / m (space group no. 11) with the lattice parameters a  = 8.96  Å ; b  = 31.93 Å; c  = 8.50 Å and β = 118.0 ° as well as 2 formula units per unit cell . Template: room group / 11

Education and Locations

Geocronite crystal aggregate from the Pollone Mine, Valdicastello Carducci, Pietrasanta , Apuan Alps (Tuscany), Italy (size: 2.7 cm × 2.4 cm × 1.3 cm)

Geokronit formed hydrothermally in ore - courses where he often shared with other sulphides and sulfosalts associated occurs, such as, among others, galena , pyrite and tetrahedrite . Barite , fluorite and quartz can also occur as accompanying minerals.

As a rather rare mineral formation, geokronite can in part be abundant, but overall it is not very common. So far (as of 2016) around 130 locations are known for Geokronit. In addition to its type locality , the Sala silver mines, the mineral was also found in Sweden in the copper mines of Falun in the province of Dalarnas län, the iron sulfide mine Sätra near Finspång in the province of Östergötland, near Storgruvan and Nordmark in the municipality of Filipstad in the province of Värmland and at Björkskogsnäs in the municipality of Hällefors .

Virgem da Lapa in the Brazilian state of Minas Gerais and Pietrasanta in the Italian province of Lucca , where crystals between 8 cm and 9 cm in size were found, are known for their extraordinary geocronite finds. After all, tabular crystals up to 4 cm in size were discovered in the lead-zinc mine “Kilbricken” near Quin in Ireland.

In Germany, the mineral could only be found in the Clara mine near Oberwolfach and the Segen Gottes mine near Wiesloch in Baden-Württemberg, in the Bayerland mine near Pfaffenreuth in the municipality of Leonberg (Upper Palatinate) in Bavaria and in the Louise mine near Bürdenbach in Rhineland- Palatinate to be discovered.

In Austria, geokronite was found in the gold mines on Radhausberg in the Gastein Valley (Hohe Tauern) and on and the Kranzlhöhe (Radstädter Tauern) in Salzburg , on the Styrian Kalkspitze and the Lungauer Kalkspitze (Schladminger Tauern) between Salzburg and Styria and in the Lead pits near Obernberg am Brenner in Tyrol.

In Switzerland, you know the mineral so far only from Turtschi, a small Dolomite - disruption in the Binn Valley , and from the quarry La Plâtrière in Granges (Lens) in the town of Sion (French immersion ) in the canton of Valais.

Other locations are in Albania, Argentina, Australia, Azerbaijan, Bolivia, Bosnia and Herzegovina, Bulgaria, China, Finland, France, Greece, India, Iran, Ireland, Italy, Japan, Canada, Kyrgyzstan, Luxembourg, Norway, Peru, Romania, Serbia, Slovakia, Taiwan, the Czech Republic, Turkey, Hungary, the United Kingdom (UK) and the United States of America (USA).

See also

literature

  • Lars Fredrik Svanberg: Undersökning of Geokronit och Hydrofit tvenne inom Sverige Förekommande nya mineralier. In: K. svenska vetenskapsakad. Handlingar Volume 3/27, 1839, p. 187 (see also German translation at digitalesthueringen.de of the Thuringian University and State Library Jena)
  • Geokronit In: Ernst Ferdinand August: Concise Dictionary of Chemistry and Physics , Volume 2, Verlag M. Simon, 1845, p. 227 in the Google book search
  • C. Doelter, H. Leitmeier (ed.): Handbuch der Mineralchemie: Volume IV First half: Sulfur compounds . Springer, Berlin [a. a.] 2013, ISBN 978-3-642-49865-7 , pp. 455–457 ( limited preview in the Google book search - originally published by Theodor Steinkopff Dresden and Leipzig 1926).
  • Richard W. Birnie, Charles W. Burnham: The crystal structure and extent of solid solution of geocronite In: American Mineralogist Volume 61 (1976, pp. 963–970) ( PDF 875 kB )
  • Helmut Schrätze, Karl-Ludwig Weiner: Mineralogy. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 299 .

Web links

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

Individual evidence

  1. ↑ a b c d C. Doelter, H. Leitmeier (Hrsg.): Handbuch der Mineralchemie: Volume IV First half: Sulfur compounds . Springer, Berlin [a. a.] 2013, ISBN 978-3-642-49574-8 , pp. 455–457 ( limited preview in the Google book search - originally published by Theodor Steinkopff Dresden and Leipzig 1926).
  2. ↑ a b c IMA / CNMNC List of Mineral Names; January 2016 (PDF 1.6 MB)
  3. ^ 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.  123 .
  4. ↑ a b c d e Geocronite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 62.9 kB )
  5. ↑ a b Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  479 (first edition: 1891).
  6. ↑ DNB personal dataset on Svanberg, Lars Fredrik
  7. ↑ Geokronit In: Ernst Ferdinand August: Handwortbuch der Chemie und Physik , Volume 2, Verlag M. Simon, 1845, p. 227 in the Google book search
  8. ↑ 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.  352 .
  9. ↑ Mindat - Number of localities for Geokronit
  10. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia . Dörfler Verlag GmbH, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 60 .
  11. ↑ Find location list for Geokronit in the Mineralienatlas and Mindat