Platarsite

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Platarsite
General and classification
other names
  • IMA 1976-050
  • Rhodium sperrylite (also Rh sperrylite)
chemical formula
  • PtAsS
  • (Pt, Rh, Ru) AsS
  • Pt (As, S) 2
Mineral class
(and possibly department) 		Sulfides and sulfosalts
System no. to Strunz
and to Dana 		2.EB.25
02.12.03.06
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  = 5.788  Å
Formula units Z  = 4
Physical Properties
Mohs hardness 7 to 7.5 ( VHN 50 = 1379–1584, average 1486)
Density (g / cm 3 ) measured: 8.0; calculated: 8.375
Cleavage not defined
colour gray in polished surfaces
Line color not defined
transparency opaque (opaque)
shine Metallic luster

Platarsite is a seldom occurring mineral from the mineral class of " sulfides and sulfosalts " with the idealized chemical composition PtAsS and therefore, chemically speaking, a platinum - arsenic- sulfide.

Platarsite crystallizes in the cubic crystal system , but has so far only been found in the form of tiny, irregular grains or triangular crystals up to about 1.1 mm in size and as inclusions in platinum nuggets , chromite and silicate minerals . The mineral is in any form opaque ( opaque ). Under the incident light microscope , polished platarsite surfaces appear gray and a little darker compared to the often coexisting sperrylite .

Etymology and history

The mineral was first mentioned in 1965 in the first description of hollingworthite by Eugen Friedrich Stumpfl (1931–2004) and Andrew M. Clark, which they did not regard as an independent mineral type, but as a rhodium- rich variety of sperrylite ( rhodium-sperrylite or Rh -Sperrylite ).

The first description of platarsite as an independent mineral was made by Louis J. Cabri, JH Gilles Laflamme and John M. Stewart on the basis of mineral samples from the platinum metal mine Onverwacht near Mashishing (until 2006 Lydenburg ) in the South African province of Mpumalanga . Cabri, Laflamme and Stewart designated the mineral after its composition Plat in, Ar sen and S chwefel, on the basis of the already known and related minerals Irarsit (IrAsS) and Osarsit (OsAsS) and submitted their results 1976 test at the International Mineralogical Association (IMA) that recognized the mineral and the chosen name that same year. The first description was published a year later in the specialist magazine The Canadian Mineralogist .

Type material of the mineral is in the Royal Ontario Museum in Toronto under the catalog no. M34681 (holotype, polished sections containing rhodium and ruthenium) and in the Canadian Museum of Nature in Ottawa (Canada), in the National Museum of Natural History of the Smithsonian Institution complex in Washington, DC (USA) under catalog no. 136485A0 and in the Fersman Museum of the Russian Academy of Sciences in Moscow (Russia) under catalog no. N79000 retained .

classification

Since the platarsite was only recognized as an independent mineral in 1976 and this was only published in 1977, it is not yet listed in the outdated 8th edition of the mineral classification according to Strunz . Only 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 , was the mineral given the system and mineral number. II / D.18-70 . In the "Lapis Classification" This also corresponds to the department "sulfides with [molar ratio] Metal: S, Se, Te <1: 1" where Platarsit with Cobaltit , Gersdorffit , Hollingworthit , Irarsit , Jolliffeit , Kalungait , Milotait , Tolovkit , Ullmannit and Willyamit form the "cobaltite group" (II / D.18) (as of 2018).

The 9th edition of Strunz's mineral systematics, which has been valid since 2001 and updated by the IMA until 2009, classifies platarsite 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 in the sub-section "M: S = 1: 2, with Fe, Co, Ni, PGE etc." according to its composition where it together with Changchengit, Cobaltit, Gersdorffit-P213 , Gersdorffit-Pa3 , Gersdorffit-Pca21 , Hollingworthit, Irarsit, Jolliffeit, Kalungait, Krutovit , Maslovit, Mayingit , Michenerit, Milotait, Padmait, 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 , assigns platarsite to the class of "sulfides and sulfosalts" and there into the category of "sulfide minerals". Here, however, 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 idealized (theoretical) composition of platarsite (PtAsS), the mineral consists of platinum (Pt), arsenic (As) and sulfur (S) in the molar ratio of metal: sulfur (or sulfur representative) = 1: 2. Arsenic as sulfur representative can be seen, was expressed by Louis J. Cabri, JH Gilles Laflamme and John M. Stewart in their first description and by JT Szymański when analyzing the crystal structure of platarsite with the formula Pt (As, S) 2 . The mass fraction (% by weight) of the elements in the pure formula is 64.6% Pt, 24.8% As and 10.6% S.

In nature, however, platinum can almost always be found mixed with other platinum metals in varying proportions. For example, the rhodium sperrylite described by Stumpfl and Clark in 1965 contained 23.8% by weight of Pt, 30.7% by weight of As and 1.8% by weight of S, and 17.8% by weight of iridium (Ir), 11.6 wt% Rh and 2.1 wt% palladium (Pd).

The microprobe analysis carried out by Cabri, Laflamme and Stewart on four platarsite grains of the type material each revealed a chemical composition in which the platinum content was higher than that of rhodium (Rh) or ruthenium (Ru). On average, the samples contained 29.7% by weight Pt (26.9-31.4), 33% by weight As and 11.2% by weight S and 11.9% by weight Rh (10, 3-13.8), 9.5% by weight Ru (8.5-11.4), 4.0% by weight Ir (0.54-6.1), 0.6% by weight Osmium (Os). This corresponds to the empirical formula Pt 0.34 Rh 0.30 Ru 0.28 Ir 0.05 Os 0.01 As 1.03 S 0.99 , the approximate formula (Pt, Rh, Ru) AsS or the idealized and End link formula PtAsS recognized by the IMA.

Crystal structure

Platarsite crystallizes cubically in the space group Pa 3 (space group no. 205) with the lattice parameter a  = 5.788  Å and four formula units per unit cell . Template: room group / 205

Education and Locations

Platarsite forms in dunites and pegmatites as well as in layered mafic intrusions and ophiolites . As accompanying minerals may include, bornite , chromite , Genkinit , Mertieit-II , Ruthenarsenit and stibiopalladinite as well as various natural Pt-Fe-Cu-Ni alloys occur.

As a rare mineral formation, platarsite could only be detected in a few places, with around 50 sites being documented so far (as of 2020). Except at its type locality Onverwacht mine at Mashishing the mineral found in South Africa in the nearby ancient platinum deposit Mooihoek ( Mooihoek Farm ) mines platinum metal in Mpumalanga, several in the district of Rustenburg the North West Province and in the platinum mining Driekop in Sekhukhuneland district about 25 km northeast of Burgersfort and the Overysel platinum deposit and the Sandsloot mine near Mokopane in the Limpopo province.

In Austria, platarsite has so far only occurred in Styria , more precisely in the municipality of Kraubath an der Mur and in an unnamed chromite mine on Mitterberg and on Sommergraben in the municipality of Sankt Stefan ob Leoben .

Locations in Germany or Switzerland are not yet known.

Other locations are in Albania, Australia, Brazil, Denmark, Finland, Greece, Greenland, India, Canada, Myanmar, Norway, Russia, Zimbabwe, Spain and the United States of America (USA). Another location in the United Kingdom is still questionable as it has not yet been confirmed.

See also

literature

  • Louis J. Cabri, JH Gilles Laflamme, John M. Stewart: Platinum-group minerals from Onverwacht. II. Platarsite, a new sulfarsenide of platinum . In: The Canadian Mineralogist . tape 15 , 1977, pp. 385–388 (English, rruff.info [PDF; 489 kB ; accessed on June 20, 2020]).
  • JT Szymański: The crystal structure of platarsite, Pt (As, S) 2 , and a comparison with sperrylite, PtAs 2 . In: The Canadian Mineralogist . tape 17 , 1979, pp. 117–123 (English, rruff.info [PDF; 588 kB ; accessed on June 21, 2020]).

Web links

Individual evidence

  1. ↑ a b c 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 June 20, 2020 .
  2. ↑ a b c d e f Louis J. Cabri, JH Gilles Laflamme, John M. Stewart: Platinum-group minerals from Onverwacht. II. Platarsite, a new sulfarsenide of platinum . In: The Canadian Mineralogist . tape 15 , 1977, pp. 385–388 (English, rruff.info [PDF; 489 kB ; accessed on June 20, 2020]).
  3. ^ 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 (English).
  4. ↑ a b c d JT Szymanski: The crystal structure of platarsite, Pt (As, S) 2 , and a comparison with sperrylite, PtAs 2 . In: The Canadian Mineralogist . tape 17 , 1979, pp. 117–123 (English, rruff.info [PDF; 588 kB ; accessed on June 21, 2020]).
  5. ↑ 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 .
  6. ^ A b 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 June 22, 2020]).
  7. ↑ a b Platarsite . 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; 60  kB ; accessed on June 20, 2020]).
  8. ↑ Catalog of Type Mineral Specimens - P. (PDF 113 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed June 22, 2020 .
  9. ↑ 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 June 20, 2020 .
  10. ↑ Localities for Platarsite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 22, 2020 .
  11. ↑ a b List of locations for platarsite in the Mineralienatlas and Mindat , accessed on June 20, 2020.