Modderite

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Modderite
General and classification
other names

Arsenic cobalt

chemical formula
  • CoAs
  • (Co, Fe) As
Mineral class
(and possibly department) 		Sulfides and sulfosalts
System no. to Strunz
and to Dana 		2.CC.15 ( 8th edition : II / B.09c)
08/02/18/01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Pmcn (No. 62, position 5)Template: room group / 62.5
Lattice parameters a  = 3.46  Å ; b  = 5.87 Å; c  = 5.29 Å
Formula units Z  = 4
Physical Properties
Mohs hardness ≈ 4 ( VHN = 26)
Density (g / cm 3 ) calculated: 8.28 (synthetic)
Cleavage not defined
colour steel gray, black, bluish white
Line color Gray
transparency opaque
shine Metallic luster

Modderite is a very rarely occurring mineral with the idealized chemical composition CoAs and is therefore chemically a cobalt arsenide, more precisely cobalt (III) arsenide , with the molar ratio of cobalt  :  arsenic  = 1: 1. Due to the chemical relationship of arsenides to sulfides Modderite belongs to the mineral class of "sulfides and sulfosalts".

Since a small part of the cobalt is usually replaced ( substituted ) by iron in naturally occurring modderites , the chemical composition is also given as a mixed formula with (Co, Fe) As in various sources. The elements indicated in round brackets can represent each other in the formula, but are always in the same proportion to the arsenic content of the mineral.

Modderite crystallizes in the orthorhombic crystal system , but has so far only been found in the form of tiny grains up to about 0.05 mm in diameter and in coarse aggregates . The mineral is generally opaque and has a metallic sheen on the surfaces of the steel-gray to black or bluish-white grains .

Etymology and history

Modderite was first discovered in the gold mines Modderfontein (also Modderfontein 'B' ) near Springs and New Modderfontein near Benoni on the Witwatersrand in what was then the South African province of Transvaal . It was first described in 1923 by Richard A. Cooper (1890–1972), who named the mineral after its type locality .

The type material of the mineral is in the National Museum of Natural History in Washington, DC in the USA under the catalog no. 161217 kept.

As a synthetic compound, the cobalt arsenide CoAs was known before the discovery of the mineral because it is easy to manufacture.

classification

In the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the modderite belonged to the mineral class of "sulphides and sulphosalts (including selenides, tellurides, arsenides, antimonides and bismuthides)" and there to the department of "sulphides with the substance ratio M: S = 1: 1 ", where he is the only member of the group of minerals of the" NiAs type and relatives "and" Slightly deformed NiAs structure "with the system no. II / B.09c .

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 / C.19-40 . In the "Lapis Classification" this is equivalent to the department "sulfides with metal: S, Se, Te ≈ 1: 1" where Modderit with Achávalit , Heideit , Jaipurit , pyrrhotite , Smythit , Troilite and Westerveldit an independent but unnamed Group forms.

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and was updated by the International Mineralogical Association (IMA) until 2009, also classifies modderite in the category of "Metal sulfides, M: S = 1: 1 (and similar)". However, this is further subdivided according to the predominant metals in the compound, so that the mineral can be found according to its composition in the sub-section "with nickel (Ni), iron (Fe), cobalt (Co) etc.", where it is named the "Westervelditgruppe" with the system no. 2.CC.15 and the other members Cherepanovit , Ruthenarsenit and Westerveldit forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the modderite to the class of "sulfides and sulfosalts" and there in the department of "sulfide minerals". Here he is the only member of the unnamed group 08/02/18 within the subsection “Sulphides - including selenides and tellurides - with the composition A m B n X p , with (m + n): p = 1: 1”.

Chemism

The theoretical composition of CoAs consists of 44.03% cobalt and 55.97% arsenic. However, natural modderite can contain up to 9% iron.

The analysis of 11 grains from the Daşkəsən Rayon (also Dashkesan ) in Azerbaijan with the electron beam microanalysis showed an average composition of 35.3 to 41.3% cobalt, 3.1 to 9.9% iron, 0.04% nickel and 55 , 9 to 57.5% arsenic. This corresponds to an idealized, empirical composition (Co 0.89 Fe 0.12 ) As.

Crystal structure

Modderite crystallizes orthorhombically in the space group Pmcn (space group no. 62, position 5) with the lattice parameters a  = 3.46  Å ; b  = 5.87 Å and c  = 5.29 Å as well as four formula units per unit cell . Template: room group / 62.5

Education and Locations

The mineral was found in the heavy mineral concentrates at its type locality Modderfontein and New Modderfontein on the Witwatersrand in South Africa . As Begleitminerale could here Alloklasit , chalcopyrite , Cobaltit , Glaukodot , Nickelin , pentlandite , pyrrhotite and safflorite be detected.

In the concentrates investigated by Paul Ramdohr , which he received from Traugott Wilhelm Gevers from Johannesburg , a mineral was found that could be modderite, but also a species-rich paragenesis of several unknown ores, which made a clear determination difficult.

The only other locations left (as of 2018) are the “Redbed” deposit Littleham Bay , a sand or clay rock that is intensely red colored by finely distributed hematite , near Budleigh Salterton in the English county of Devon and the lead-zinc-cobalt-nickel -Lagerstätte Kalangu at Tamu-Kalangu belt in a circle Akto the Kyrgyz Autonomous Prefecture Kizilsu (also Kezilesu ) known in China.

use

Synthetically produced modderite (cobalt (III) arsenide) is used as a semiconductor and in photo-optical devices.

See also

literature

  • RA Cooper: Mineral constituents of Rand concentrates . In: Journal of the Chemical, Metallurgical, and Mineralogical Society of South Africa . tape 24 , 1923, pp. 90-95 .
  • William F. Foshag: New Minerals: Doubtful species. Class: Sulphides, etc. In: American Mineralogist. Journal Mineralogical Society of America . tape 11 , no. 3 , 1926, pp. 77-78 ( minsocam.org [PDF; 120 kB ; accessed on September 23, 2019]).
  • Michael Fleischer , Louis J. Cabri: New Mineral Names . In: American Mineralogist . tape 63 , no. 5-6 , 1978, pp. 598–600 ( minsocam.org [PDF; 326 kB ; accessed on June 4, 2018]).

Web links

Individual evidence

  1. ↑ 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.  331 .
  2. ↑ a b Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: September 2019. (PDF 2672 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, September 2019, accessed September 23, 2019 .
  3. ↑ a b c d 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.  87 .
  4. ↑ David Barthelmy: Modderite Mineral Data. In: webmineral.com. Retrieved September 23, 2019 .
  5. ↑ a b c d e f g Modderite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 59  kB ; accessed on September 23, 2019]).
  6. ↑ 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 .
  7. ^ A b Richard V. Gaines, H. Catherine W. Skinner, Eugene E. Foord, Brian Mason , Abraham Rosenzweig: Dana's New Mineralogy . 8th edition. John Wiley & Sons, New York (et al.) 1997, ISBN 0-471-19310-0 , pp. 82 .
  8. ↑ Cooperite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 61  kB ; accessed on September 23, 2019]).
  9. ↑ Catalog of Type Mineral Specimens - M. (PDF 124 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed September 23, 2019 .
  10. ^ A b Paul Ramdohr : The ore minerals and their adhesions . 4th, revised and expanded edition. Akademie-Verlag, Berlin 1975, p.  673 .
  11. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed September 23, 2019 .
  12. ↑ AI Makhmudov, IP Laputina: First occurrence of modderite in the USSR . In: Zapiski Vsesoyuznogo Mineralogicheskogo Obshchestva . tape 106 , 1977, pp. 347-350 (Russian).
  13. ↑ Michael Fleischer , Louis J. Cabri: New Mineral Names . In: American Mineralogist . tape  63 , no. 5-6 , 1978, pp. 598–600 ( minsocam.org [PDF; 318 kB ; accessed on September 23, 2019]).
  14. ↑ Rudolf Graubner: Lexicon of Geology, Minerals and Rocks . Emil Vollmer Verlag, Munich 1980, ISBN 3-87876-327-1 , p. 321 .
  15. ↑ Find location list for modderite in the Mineralienatlas and Mindat ( accessed September 23, 2019)
  16. ↑ cobalt (III) arsenides. In: americanelements.com. American Elements, accessed September 23, 2019 .