Troilit

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Troilit
Sikhote alin.jpg
Troilite inclusions in the Sikhote Alin meteorite
General and classification
chemical formula FeS
Mineral class
(and possibly department) 		Sulfides and sulfosalts
System no. to Strunz
and to Dana 		2.CC.10 ( 8th edition : II / B.09a)
08/02/09/01
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol ditrigonal-dipyramidal; 6 m 2
Space group P 6 2 c (No. 190)Template: room group / 190
Lattice parameters a  = 5.962  Å ; c  = 11.750 Å
Formula units Z  = 12
Physical Properties
Mohs hardness 3.5 to 4.5
Density (g / cm 3 ) measured: 4.67 to 4.79; calculated: 4.85
Cleavage is missing
Break ; Tenacity uneven
colour gray-brown, bronze-yellow to bronze-brown; quickly turning dark when exposed to light
Line color brownish black
transparency opaque (opaque)
shine Metallic luster

Troilite , also known as pyrite or Meteor gravel is known a relatively rare because almost exclusively in meteorites occurring mineral from the mineral class of "sulfides and sulfosalts". It crystallizes in a hexagonal crystal system with the chemical composition FeS and thus, chemically speaking, iron (II) sulfide .

In iron meteorites , Troilit develops microcrystalline, granular to coarse aggregates of gray-brown or bronze-yellow to bronze-brown color and a metallic sheen on the surfaces. When exposed to moist air, the mineral quickly darkens and becomes cloudy.

Etymology and history

Troilite as striking, bright shiny mineral in was very early meteorites discovered and as pyrite or Meteor gravel referred. It was finally named by Wilhelm von Haidinger after the Italian Jesuit Dominico Troili (1722–1792), who worked as a physicist in Modena and was one of the first to describe the shiny yellow mineral. He found it in the olivine - hypersthene - chondrite Albareto , which fell on July 6, 1766 near the city ​​of the same name in the Italian province of Modena .

classification

Already in the outdated 8th edition of the mineral classification according to Strunz , the Troilit belonged to the mineral class of "sulfides and sulfosalts" and there to the department of "sulfides with [the substance ratio ] M: S = 1: 1" (NiAs type and relatives), where he together with Achávalit , Breithauptit , Freboldit , Imgreit , Jaipurit , Kotulkit , Langisit , Nickelin , pyrrhotite , Sederholmit and Smythit the "NiAs-series" with the system number. II / B.09a .

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.19-10 . In the "Lapis Classification" equivalent to the also department "sulfides with metal: S, Se, Te ≈ 1: 1" where Troilite with Achávalit, Heideit , Jaipurit, Modderit , pyrrhotite, Smythit and Westerveldit an independent but unnamed Group forms.

The 9th edition of Strunz's mineral systematics , which has been valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, also classifies the Troilit in the category of "Metal sulfides, M: S = 1: 1 (and similar)". This is, however, further subdivided according to the predominant metals in the compound, so that the mineral can be found in the sub-section "with nickel (Ni), iron (Fe), cobalt (Co) etc.", where it is only together with pyrrhotite and smythite the "pyrrhotic group" with the system no. 2.CC.10 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Troilit 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 02.08.09 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 idealized chemical composition of Troilit (FeS) consists of 63.53% by weight iron (Fe) and 36.47% by weight sulfur (S).

In contrast to the terrestrial pyrrhotite , the chemical analysis of the Troilit always shows the atomic ratio of 50% iron (Fe) and 50% sulfur (S), with small amounts of cobalt and nickel being added to the iron. In the case of pyrrhotite, there is always a deficit of iron in the formula up to Fe 5 S 6 (on average Fe 11 S 12 ). The reason for this is that iron and sulfur are always in stoichiometric equilibrium in the meteoritic troilite , but not in the earthly pyrrhotite.

Crystal structure

Troilit crystallizes hexagonally in the space group P 6 2 c (space group no. 190) with the lattice parameters a  = 5.962  Å and c  = 11.750 Å as well as twelve formula units per unit cell . Template: room group / 190

properties

Pure Troilit is paramagnetic .

Like the other minerals of the pyrrhotine group, troilite is generally difficult to dissolve in acids or alkalis . The reaction to nitric acid (HNO 3 ) is very weak and rather low to aqua regia . It can only be removed from hydrochloric acid (HCl) if it has been heated or is in vapor form. The effects of potassium hydroxide (KOH) cause the surfaces to become iridescent.

Modifications and varieties

Troilit is the high-temperature modification of iron sulfide and is only stable above about 300 ° C.

Education and Locations

Troilite occurs as a secondary part in almost all meteorite types and occurs there mostly in paragenesis with taenite and kamacite . Chondrites , the most common class of meteorites, contain around 5% troilite in the form of small (up to around 1 mm) irregular grains. In iron meteorites , troilite occurs in cm-large inclusions, often together with graphite . Also Achondrite contain Troilite as small grains.

The mineral was found in the following meteorites and their impact craters:

The Nyiragongo volcano near Goma in the Democratic Republic of the Congo is one of the few purely terrestrial sites for Troilit.

See also

literature

  • 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. 74 .

Web links

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

Individual evidence

  1. ↑ a b c d Howard T. Evans Jr .: Lunar Troilite: Crystallography . In: Science . tape 167 , no. 3918 , February 1970, p. 621–623 , doi : 10.1126 / science.167.3918.621 , bibcode : 1970GeCAS ... 1..399E (English).
  2. ↑ a b c d Troilite . 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; 58  kB ; accessed on April 30, 2019]).
  3. ↑ a b c d 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 .
  4. ^ A b Paul Ramdohr : The ore minerals and their adhesions . 4th, revised and expanded edition. Akademie-Verlag, Berlin 1975, p.  635 .
  5. ↑ Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 335 .
  6. ↑ a b Marco E. Ciriotti, Lorenza Fascio , Marco Pasero : Italian Type Minerals . 1st edition. Edizioni Plus - Università di Pisa, Pisa 2009, ISBN 978-88-8492-592-3 , p. 271 .
  7. ^ MW Haidinger: The meteorite from Albareto in the kk Hof-Mineraliencabinet, from the year 1766, and the Troilit . In: Meeting reports of the Imperial Academy of Sciences . tape 47 , 1863, p. 283–298 ( available online at rruff.info [PDF; 1,2 MB ; accessed on April 30, 2019]).
  8. ^ Meteoritical Bulletin Database - Albareto. In: lpi.usra.edu. The Meteoritical Society, accessed April 30, 2019 .
  9. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed April 30, 2019 .
  10. ↑ David Barthelmy: troilite MineralData. In: webmineral.com. Retrieved April 30, 2019 .
  11. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  445 (first edition: 1891).
  12. ↑ Paul Ramdohr : The ore minerals and their adhesions . 4th, revised and expanded edition. Akademie-Verlag, Berlin 1975, p.  635 .
  13. ↑ Find location list for Troilit in the Mineralienatlas and Mindat
  14. ↑ Type locality Mt Nyiragongo, Goma, Kivu, Democratic Republic of Congo (Zaïre). In: mindat.org. Hudson Institute of Mineralogy, accessed April 30, 2019 .