Hollingworthite

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Hollingworthite
General and classification
other names

IMA 1964-029

chemical formula
  • RhAsS
  • (Rh, Pt, Pd) AsS
Mineral class
(and possibly department)
Sulfides and sulfosalts
System no. to Strunz
and to Dana
2.EB.25 ( 8th edition : II / C.06c)
02.12.03.08
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic-disdodecahedral; 2 / m  3
Space group Pa 3 (No. 205)Template: room group / 205
Lattice parameters a  = 5.77  Å
Formula units Z  = 4
Physical Properties
Mohs hardness 6.5 to 7 ( VHN 100 = ∼650–700 kg / mm 2 )
Density (g / cm 3 ) calculated: 7.86
Cleavage not defined
colour medium gray on polished surfaces, slightly bluish in oil
Line color not defined
transparency opaque (opaque)
shine Metallic luster

Hollingworthite is a relatively seldom occurring mineral from the mineral class of " sulfides and sulfosalts " with the idealized chemical composition RhAsS and therefore, chemically speaking, a rhodium - arsenic sulfide.

Hollingworthit crystallizes in the cubic crystal system and is usually found in the form of small, idiomorphic to irregular grains microns to about 40 size which closely with rhodiumreichem and rhodiumfreiem Sperrylith and Geversit are fused. The mineral, which is opaque in every form, shows a metallic sheen on the surfaces of the medium-gray, in oil also slightly bluish, crystallites on polished surfaces .

Etymology and history

Hollingworthite was first discovered in the Driekop platinum mine in the Sekhukhuneland district about 25 km northeast of Burgersfort in the Bushveld complex in South Africa . It was first described in 1965 by Eugen Friedrich Stumpfl (1931-2004) and Andrew M. Clark. They named the mineral after the then professor of geology at University College London (England) Sidney Ewart Hollingworth (1899-1966) to honor his contribution to the study of the geology of the Pleistocene in the north of the United Kingdom .

The type material of the mineral is kept at the Mines ParisTech (English National School of Mines ) in Paris .

classification

Already in the outdated 8th edition of the mineral classification according to Strunz , the hollingworthite belonged to the mineral class of "sulphides and sulphosalts" and there to the division of "sulphides with [the substance ratio] M: S <1: 1", where together with Irarsite it was the " Hollingworthit series “with the system no. II / C.06c .

In the Lapis mineral directory according to Stefan Weiß, which, out of consideration for private collectors and institutional collections, is still based on this old form of Karl Hugo Strunz's system , the mineral was given the system and mineral number. II / D.18-50 . In the "Lapis Classification" This also corresponds to the department "sulfides with metal: S, Se, Te <1: 1" where Hollingworthit with Cobaltit , Gersdorffit , Irarsit, Jolliffeit , Kalungait , Milotait , Platarsit , Tolovkit , Ullmannit and Willyamit forms the "cobaltite group" (as of 2018).

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 hollingworthite in the newly defined division of "metal sulfides with a molar ratio of 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 can be found according to its composition in the sub-section "M: S = 1: 2, with Fe, Co, Ni, PGE etc.", where it together with Changchengit , cobaltite, Gersdorffit-P2 1 3 , Gersdorffit-Pa 3 , Gersdorffit-Pca2 1 , Irarsit, Jolliffeit, Kalungait, Krutovit , Maslovit , Mayingit , Michenerit , Milotait, Padmait , Platarsit, Testibiopalladit , Tolovkit, Ullmannit and Willyamit the "Gersdorffitgruppe" with the system no. 2.EB.25 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , also assigns hollingworthite to the class of "sulfides and sulfosalts" and there in the department of "sulfide minerals". Here it is in the " cobaltite group (cubic or pseudocubic crystals) " with the system no. 02.12.03 within the subsection "Sulphides - including selenides and tellurides - with the composition A m B n X p , with (m + n): p = 1: 2".

Chemism

According to the ideal (theoretical) composition of Hollingworthite (RhAsS), the mineral consists of rhodium (Rh), arsenic (As) and sulfur (S) in a molar ratio of 1: 1: 1. This corresponds to a mass fraction (% by weight) of 49.030% Rh, 35.695% As and 15.275% S.

The microprobe analyzes of the type material from the Driekop mine, however, showed different contents of 30.8% Rh, 32.6% As and 13.9 S as well as 10.3% platinum (Pt), 8.7% palladium (Pd) and 3.1% iridium (Ir), which represents part of the original elements ( substitution , diadochy).

The analysis of hollingworthite samples from the Putorana Mountains near Norilsk in the north of the Russian Krasnoyarsk region showed similar deviations of 25.0% Rh, 35.0% As and 11.0% S as well as an additional 20.0% Pt, 5, 0% Ir and 4.0% ruthenium (Ru).

Further finds of hollingworthite on the Shetland Islands belonging to Scotland revealed a composition of 47.62% Rh, 37.02% As and 14.99% S as well as an additional 0.56% iron (Fe).

Due to the significant proportions of platinum and palladium as representatives of rhodium, the mixed formula (Rh, Pt, Pd) AsS is given in various sources for the composition of hollingworthite.

Hollingworthit also forms Irarsit (IrAsS) a complete solid solution , which may be one reason for the usually encountered iridium content in the analyzed mineral samples.

Crystal structure

Hollingworthite crystallizes cubically in the pyrite structure in the space group Pa 3 (space group no. 205) with the lattice parameter a  = 5.77  Å and four formula units per unit cell . Template: room group / 205

properties

The Mohs hardness of hollingworthite is 6.5 to 7, which corresponds to a Vickers hardness (VH, English VHN) of about 650-700 kg / mm 2 at a test force of 100 grams and is higher than that of sperrylite . In contrast, its reflectivity is significantly lower than that of Sperrylith.

Education and Locations

Hollingworthit forms in platinum deposits and is found among others in dunite - chimneys , layered ultramafic intrusions , Chromatiten and Cu-Ni sulphide ores. As Begleitminerale occurred on its type locality of, Driekop -Mine in Sekhukhuneland next Sperrylith and Geversit , nor with whom he appears closely bound there Erlichmanit , Iarsit and several platinum and iron compounds such as there is also the first time discovered Stumpflit (PTSD) or rare natural platinum-iron alloy tulameenite on. Other well-known sites in South Africa include various pits and prospections in the municipality of Mokopane in the Limpopo province, the platinum metal mines Onverwacht and Mooihoek Farm 255 KT in the area of Mashishing ( Lydenburg until 2006 ) in the Mpumalanga province and the gold fields in the Witwatersrand .

Depending on the location, other parageneses can occur such as chalcopyrite , cobaltite , gersdorffite and pyrrhotite in the Giant Mascot Mine near Hope as well as on Grasshopper Mountain and at a soap deposit on the Tulameen River in Canada or Braggite , pentlandite , pyrite and gold-silver alloys in Stillwater -Complex in the south of the US state of Montana .

Hollingworthite is one of the rather rare mineral formations, which in some cases may be abundant at different sites, but are generally not very common. So far, only a little more than 130 locations for Hollingworthite have been documented.

The only location in Germany so far is a fluvial soap deposit with solid gold and platinum metals on the Danube near Straubing in Lower Bavaria.

In Austria, the mineral has so far only been found as tiny inclusions together with other minerals of the platinum group in rounded blackish spinels near Wolfsbach in the municipality of Drosendorf-Zissersdorf in Lower Austria and in mineral samples from the ultramafic ore body, consisting of dunite and serpentinite , near Kraubath the Mur , in an unnamed pit on the Mitterberg and on the Sommergraben in the Styrian municipality of Sankt Stefan ob Leoben .

Other locations are in Albania, Argentina, Ethiopia, Botswana, Brazil, Bulgaria, China, Denmark, the Ivory Coast, Finland, France, Greece, India, Japan, other regions of Canada, the Democratic Republic of the Congo, on Cuba, in Madagascar, Mexico, Myanmar, Norway, several regions of Russia, Serbia, Zimbabwe, Slovakia, Spain and other states of the USA.

See also

literature

  • EF Stumpel, AM Clark: Hollingworthite, a new rhodium mineral, identified by electron probe microanalysis . In: American Mineralogist . tape 50 , 1965, pp. 1068-1074 (English, rruff.info [PDF; 493 kB ; accessed on April 30, 2020]).
  • Mahmud Tarkian, Hazel Margaret Prichard: Irarsite-hollingworthite solid-solution series and other associated Ru-, Os-, Ir-, and Rh-bearing PGM's from the Shetland ophiolite complex . In: Mineralium Deposita . tape 22 , 1987, pp. 178-184 , doi : 10.1007 / BF00206607 , bibcode : 1987MinDe..22..178T (English).

Web links

Individual evidence

  1. a b c d Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: March 2020. (PDF; 2.44 MB) In: cnmnc.main.jp . IMA / CNMNC, Marco Pasero, March 2020, accessed April 30, 2020 .
  2. 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.  105 (English).
  3. a b c d e Stefan Weiss: The great 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 .
  4. a b c d e f g h i j k Hollingworthite . 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; 61  kB ; accessed on April 30, 2020]).
  5. ^ John Bowles: Obituary Eugen Friedrich Stumpfl, 1931-2004. (PDF; 660 kB) In: cambridge.org. University of Cambridge , accessed March 30, 2020 .
  6. Hollingworthite. In: mindat.org. Hudson Institute of Mineralogy, accessed April 30, 2020 .
  7. Catalog of Type Mineral Specimens - H. (PDF 81 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed April 30, 2020 .
  8. Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF; 1.82 MB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed April 30, 2020 .
  9. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  260 .
  10. ^ EF Stumpfl, AM Clark: Hollingworthite, a new rhodium mineral, identified by electron probe microanalysis . In: American Mineralogist . tape 50 , 1965, pp. 1068-1074 (English, rruff.info [PDF; 493 kB ; accessed on April 30, 2020]).
  11. Type locality Driekop mine, Sekhukhuneland, Burgersfort, Limpopo, South Africa. In: mindat.org. Hudson Institute of Mineralogy, accessed April 30, 2020 .
  12. Localities for Hollingworthite. In: mindat.org. Hudson Institute of Mineralogy, accessed April 30, 2020 .
  13. List of localities for hollingworthite from the Mineralienatlas and Mindat , accessed on April 30, 2020.