Bornhardtite

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Bornhardtite
General and classification
chemical formula
  • Co 2+ Co 3+ 2 Se 4
  • Co 3 Se 4
Mineral class
(and possibly department) 		Sulfides and sulfosalts (including selenides, tellurides, arsenides, antimonides, and bismuthides)
System no. to Strunz
and to Dana 		2.DA.05 ( 8th edition : II / D.01)
02.10.01.05
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Fd 3 m (No. 227)Template: room group / 227
Lattice parameters a  = ≈ 10.2  Å
Formula units Z  = 8
Physical Properties
Mohs hardness ≈ 4
Density (g / cm 3 ) calculated: 6.166
Cleavage not defined
colour copper-pink to rose-red
Line color not defined
transparency opaque
shine Metallic luster

Bornhardtite is a very seldom occurring mineral from the mineral class of "sulfides and sulfosalts" (and relatives, see classification ) with the chemical composition Co 2+ Co 3+ 2 Se 4 , also Co 3 Se 4 for simplicity . From a chemical point of view, Bornhardtite is therefore a cobalt - selenide and the selenium analogue of Linneit . Structurally, however, both belong to the group of spinels .

Bornhardtite crystallizes in the cubic crystal system . So far, however, it has only been found in microcrystalline form in the form of massive mineral aggregates , whose copper-pink to rose-red, sometimes pink-white, surfaces have a metallic sheen .

Etymology and history

Bornhardtite was discovered for the first time together with trogtalite , hastite (discredited, identical to ferroselite) and a cobalt selenide ( known as freboldite from 1957 ) in the Trogtal quarry near Lautenthal in the Lower Saxony district of Goslar . It was first described in 1955 by Paul Ramdohr and Marg. Schmitt, who named the mineral after the German geologist, explorer, mining official and mining historian Wilhelm Bornhardt .

A storage place for the type material of Bornhardtit is not defined.

Bornhardtite was already known before the International Mineralogical Association (IMA) was founded in 1958 and was mostly recognized as a mineral in the professional world. As a so-called grandfathered mineral (G), Bornhardtite was recognized as an independent mineral type by the Commission on new Minerals, Nomenclature and Classification (CNMNC).

classification

The current classification of the IMA counts the Bornhardtite to the spinel supergroup , where together with Trüstedtite and Tyrrellite it forms the Bornhardtite subgroup within the Selenospinelle.

Already in the outdated but still partially in use 8th edition of the mineral classification by Strunz of Bornhardtit belonged to the mineral class of "sulfides and sulfosalts" and then to the Department of "sulfides with [molar ratio] Metal: S, Se, Te <1: 1 "where he together with Cadmoindit , Carrollit , daubréelite , Fletcherit , Florensovit , greigite , Indit , Kalininit , linnaeite , Polydymit , Siegenit , Trüstedtit, Tyrrellit and Violarite the" linnaeite group "with the system number. II / D.01 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), classifies Bornhardtite in the category of “Metal sulfides with M: S = 3: 4 and 2: 3”. This is also further subdivided according to the precise molar ratio, so that the mineral according to its composition in the subsection "M: S = 3: 4" can be found, where it together with Cadmoindit, Carrollit, Cuproiridsit , Cuprorhodsit , daubréelite, Ferrorhodsit , Fletcherit , Florensovit, greigite, Indit, Kalininit, linneite, Malanit , Polydymit, Siegenit, Trüstedtit, Tyrrellit, Violarite and Xingzhongit the "Linneitgruppe" system no. 2.DA.05 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Bornhardtite to the class of "sulfides and sulfosalts" and there in the department of "sulfide minerals". Here he is in the "Linneit group (isometric: Fd 3 m )" with the system no. 02.10.01 within the subsection " Sulphides - including selenides and tellurides - with the composition A m B n X p , with (m + n): p = 3: 4 ". Template: room group / 227

Chemism

The chemical compound Co 2+ Co 3+ 2 Se 4 consists of 42.74% cobalt and 57.26% selenium . A precise chemical analysis of the type material does not seem to have been carried out so far.

Crystal structure

Bornhardtite crystallizes cubically in the space group Fd 3 m (space group no. 227) with the lattice parameter a  = 10.2  Å and 8 formula units per unit cell . Template: room group / 227

Education and Locations

At its type locality , the Trogtal quarry in the district of Goslar in Lower Saxony, Bornhardtite was found to be associated with Trogtalite, Hastite and another unnamed cobalt selenide in the form of fine, purple to red-brown adhesions in Clausthalite . Hematite and genuine selenium were documented here as additional accompanying minerals . In the in greywacke be built next to the quarry was selenerzführenden dolomite - courses also iron ore found.

In addition to the Trogtal quarry, the mineral was discovered in Lower Saxony in the former Weintraube iron ore mine near Lerbach in the Göttingen district. It was also found in the selenium ores near Tilkerode / Abberode in the Mansfeld-Südharz district of Saxony-Anhalt and in the selenium mineralization of the Friedrichsglück mine in the Tannenglasbachsgrund near Neustadt am Rennsteig in the Thuringian Forest .

In Argentina we know Bornhardtit also from Cerro de Cacheuta in the province of Mendoza belonging Sierra de Cacheuta and from the uranium - deposit Pinky Fault in the Canadian province of Saskatchewan .

See also

literature

Web links

Individual evidence

  1. ↑ a b c IMA / CNMNC List of Mineral Names; March 2018 (PDF 1.65 MB)
  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.  93 (English).
  3. ↑ a b Webmineral - Bornhardtite (English)
  4. ↑ a b c d e Bornhardtite . 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; 59  kB ; accessed on September 25, 2018]).
  5. ↑ 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. ↑ 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. 100 .
  7. ^ Hugo Strunz : Mineralogical tables . 3. Edition. Geest & Portig, Leipzig 1957, p.  98 (NiAs type and related: Freboldit).
  8. ↑ Cristian Biagioni, Marco Pasero: The systematics of the spinel-type minerals: An overview . In: American Mineralogist . tape 99 , no. 7 , 2014, p. 1254–1264 , doi : 10.2138 / am.2014.4816 (English, preliminary version online [PDF]).
  9. ↑ Michael Fleischer : New Mineral Names . In: American Mineralogist . tape  41 , no. 1-2 , 1956, pp. 164 ( minsocam.org [PDF; accessed September 28, 2018]).
  10. ↑ Mineralienatlas : Trogtal quarry
  11. ↑ Find location list for Bornhardtite at the Mineralienatlas and at Mindat