Ahrensite

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Ahrensite
General and classification
other names

IMA 2013-028

chemical formula
  • SiFe 2 O 4
  • γ-Fe 2 (SiO 4 )
  • (Fe 2+ , Mg) [SiO 4 ]
Mineral class
(and possibly department) 		Silicates and germanates - island silicates (nesosilicates)
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  = 8.1629 (2) (synthetic 8.234 (1))  Å
Formula units Z  = 8
Physical Properties
Mohs hardness 6th
Density (g / cm 3 ) calculated: 4.26
Cleavage not defined
colour bluish green or colorless
Line color White
transparency translucent
shine not defined

Ahrensite is a very seldom occurring mineral from the mineral class of "silicates and germanates" with the idealized chemical composition γ-Fe 2 (SiO 4 ) and thus chemically an iron silicate . Structurally, however, ahrensite, like its Mg analogue ringwoodite (Mg 2 SiO 4 ), belongs to the island silicates on the one hand and to the spinel supergroup on the other . Correspondingly, the chemical composition can also be specified in the formula notation customary for spinels with SiFe 2 O 4 .

Ahrensite crystallizes in the cubic crystal system , but has so far only been discovered in microcrystalline form at the grain boundaries of olivine crystals enclosed in the meteorite material. In the light microscope Ahrensit appear translucent bluish green. But it can also be colorless.

Etymology and history

The synthetic equivalent of ahrensite (γ-Fe 2 SiO 4 ) was already shown in 1974 and structurally analyzed by Takehiko Yagi, Fumiyuki Marumo and Syun-Iti Akimoto.

Ahrensite was first discovered as a natural mineral formation on July 18, 2011 near Tissint in the Moroccan province of Tata , the Martian meteorite of the same name . In addition to the ahrensite, Chenmingite ( IMA 2017-036 ) and Tissintite ( IMA 2013-027 ) were also found in this meteorite for the first time. The investigation of the meteorite and the first description of the newly discovered mineral was carried out in a team by Chi Ma, John R. Beckett, George R. Rossman, Oliver Tschauner, Yang Liu, Stanislav V. Sinogeikin, Jesse S. Smith and Lawrence A. Taylor. The researchers chose the name Ahrensite in honor of Caltech geophysicist Thomas J. Ahrens (1936-2010) in memory of his pioneering and fundamental contributions to high pressure mineral physics and planetary science, many of which were used to interpret shock effects in natural rocks and synthetic materials are used.

The test results for the initial description of the mineral and its chosen name were submitted for examination to the International Mineralogical Association (IMA) in 2013 (internal entry number of the IMA: 2013-028 ), which recognized the ahrensite as an independent mineral species. The first description was published in 2016 in the journal Geochimica et Cosmochimica Acta .

The type material of the mineral, which is in the sections UT1, UT2 and UT3 (2013 by Baziotis et al. Also referred to as MT-1, -2 and -3) is in the meteorite collection of the Frank H. McClung Museum at the University of Tennessee in Knoxville, USA.

classification

The current classification of the IMA is one of the Ahrensit to spinel supergroup , where he together with Brunogeierit , Filipstadit , Qandilit , ringwoodite and Ulvöspinell forms the Ulvöspinell subgroup within the Oxispinelle.

Ahrensite was only recognized as an independent mineral type by the IMA in 2013. The mineral does not appear in the outdated 8th edition of the mineral classification according to Strunz . For this reason, an exact group assignment in the 9th edition of Strunz's mineral systematics , the last update of which was made with the publication of the IMA list of mineral names in 2009, is not yet known.

Only in the "Lapis Mineralienverzeichnis", which was last published in 2018, which, out of consideration for private collectors and institutional collections, is still based on the classical systematics of Karl Hugo Strunz in the 8th edition, the mineral received the system no. VIII / A.6-30 . In this classification, the mineral, together with ringwoodite and wadsleyite, would be a member of the unnamed group VIII / A.06 within the island silicates (nesosilicates)

Chemism

The idealized compound Fe 2 SiO 4, which is the theoretical end link of the mixed ahrensite-ringwoodite series, consists of 54.81% by weight of iron, 13.78% by weight of silicon and 31.41% by weight of oxygen .

However, seven electron beam microanalyses on the type material from the Tissint meteorite showed an average composition of 43.8% FeO, 34.9% SiO 2 , 21.1% MgO and 0.75% MnO as well as traces of TiO 2 , Al 2 O 3 , CaO, Na 2 O, K 2 O and Cr 2 O 3 . Based on 4 oxygen atoms, the empirical formula is accordingly (Fe 1.06 Mg 0.91 Mn 0.02 ) Si 1.01 O 4 , which has been simplified to (Fe, Mg) 2 SiO 4 .

Crystal structure

Ahrensite crystallizes isotypically with ringwoodite in the cubic crystal system in the space group Fd 3 m (space group no. 227) with the lattice parameter a  = 8.1629 (2)  Å and 8 formula units per unit cell . Template: room group / 227

Education and Locations

Ahrensite is formed by transforming the fayalite-rich edges of olivine crystals and other iron-rich fragments in contact with shock melting pockets. In addition to the already mentioned minerals ringwoodite, olivines and pyroxenes, bridgmanite , ilmenite , pigeonite and wüstite as well as the glass maskelynite formed by impact metamorphosis and in it the pyroxene tissueintite were discovered as accompanying minerals in the analyzed thin sections .

Its type locality is the Martian meteorite Tissint from the group of shergottites within the class of achondrites , that is, it belongs to the primitive stone meteorites and consists mainly of a fine-grain pyroxene base mass without embedded silicate spheres ( chondrules )

Apart from Tissint, only the Khatyrka meteorite, discovered in the Chukchi Autonomous Okrug in the Russian Federation of Far East, and the Umbarger meteorite, discovered in the city ​​of the same name in Randall County of the US state of Texas, have been documented as ahrensite sites.

See also

literature

  • Takehiko Yagi, Fumiyuki Marumo, Syun-Iti Akimoto: Crystal structures of spinel polymorphs of Fe 2 SiO4 and Ni 2 SiO 4 . In: American Mineralogist . tape 59 , 1974, pp. 486–490 (English, rruff.info [PDF; 518 kB ; accessed on September 8, 2018]).
  • Larry W. Finger, Robert M Hazen, Takehiko Yagi: Crystal structures and electron densities of nickel and iron silicate spinels at elevated temperature or pressure . In: American Mineralogist . tape 64 , 1979, pp. 1002–1009 (English, rruff.info [PDF; 826 kB ; accessed on September 8, 2018]).
  • PA Williams, f. Hatert, M. Pasero, SJ Mills: IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) - Newsletter 16 . In: Mineralogical Magazine . tape 77 , no. 6 , August 2013, p. 2695–2709 (English, main.jp [PDF; 144 kB ; accessed on September 9, 2018]).
  • Chi Ma, Oliver Tschauner, John R. Beckett, Yang Liu, George R. Rossman, Stanislav V. Sinogeikin, Jesse S. Smith, Lawrence A. Taylor: Ahrensite, γ-Fe2SiO4, a new shock-metamorphic mineral from the Tissint meteorite : Implications for the Tissint shock event on Mars . In: Geochimica et Cosmochimica Acta . tape 184 , July 2016, p. 240–256 , doi : 10.1016 / j.gca.2016.04.042 (English).
  • William E. Glassley, John A. Korstgård, and Kai Sørensen: Further observations related to a possible occurrence of terrestrial ahrensite . In: American Mineralogist . tape 101 , no. October 10 , 2016, p. 2347–2350 , doi : 10.2138 / am-2016-5899 (English, degruyter.com [PDF; 1.3 MB ; accessed on September 9, 2018]).

Web links

Individual evidence

  1. ↑ a b c IMA / CNMNC List of Mineral Names; March 2018 (PDF 1.65 MB)
  2. ↑ a b IMA / CNMNC List of Mineral Names; March 2018 (English, PDF 1.7 MB)
  3. ↑ a b Chi Ma, Oliver Tschauner, John R. Beckett, Yang Liu, George R. Rossman, Stanislav V. Sinogeikin, Jesse S. Smith, Lawrence A. Taylor: Ahrensite, γ-Fe2SiO4, a new shock-metamorphic mineral from the Tissint meteorite: Implications for the Tissint shock event on Mars . In: Geochimica et Cosmochimica Acta . tape 184 , July 2016, p. 240–256 , doi : 10.1016 / j.gca.2016.04.042 (English).
  4. ↑ a b c d e f 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 .
  5. ↑ a b Takehiko Yagi, Fumiyuki Marumo, Syun-Iti Akimoto: Crystal structures of spinel polymorphs of Fe 2 SiO4 and Ni 2 SiO 4 . In: American Mineralogist . tape 59 , 1974, pp. 486–490 (English, rruff.info [PDF; 518 kB ; accessed on September 8, 2018]).
  6. ↑ a b c Chi Ma, Oliver Tschauner, John R. Beckett, Yang Liu, George R. Rossman, Stanislav V. Sinogeikin, Jesse S. Smith, Lawrence A. Taylor: Ahrensite, γ-Fe2SiO4, a new shock-metamorphic mineral from the Tissint meteorite: Implications for the Tissint shock event on Mars . In: Geochimica et Cosmochimica Acta . tape 184 , July 2016, p. 245 , doi : 10.1016 / j.gca.2016.04.042 (English).
  7. ↑ a b c Chi Ma, Oliver Tschauner, John R. Beckett, Yang Liu, George R. Rossman, Stanislav V. Sinogeikin, Jesse S. Smith, Lawrence A. Taylor: Ahrensite, γ-Fe2SiO4, a new shock-metamorphic mineral from the Tissint meteorite: Implications for the Tissint shock event on Mars . In: Geochimica et Cosmochimica Acta . tape 184 , July 2016, p. 244 , doi : 10.1016 / j.gca.2016.04.042 (English).
  8. ↑ a b Chi Ma, Oliver Tschauner, John R. Beckett, Yang Liu, George R. Rossman, Stanislav V. Sinogeikin, Jesse S. Smith, Lawrence A. Taylor: Ahrensite, γ-Fe2SiO4, a new shock-metamorphic mineral from the Tissint meteorite: Implications for the Tissint shock event on Mars . In: Geochimica et Cosmochimica Acta . tape 184 , July 2016, p. 241 , doi : 10.1016 / j.gca.2016.04.042 (English).
  9. ↑ 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]).
  10. ↑ IMA / CNMNC List of Mineral Names September 2009 (PDF 1.8 MB with the last official Strunz classification)
  11. ↑ Meteoritical Bulletin Database - Tissint (English)
  12. ↑ Find location list for ahrensite at the Mineralienatlas and at Mindat