Ringwoodite

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Ringwoodite
BlueRingwoodite.jpg
Bluish ringwoodite crystal (size ≈ 150 μm)
General and classification
other names

IMA 1968-036

chemical formula
  • SiMg 2 O 4
  • γ- (Mg, Fe 2+ ) 2 [SiO 4 ]
  • Mg 2 (SiO 4 )
Mineral class
(and possibly department)
Silicates and germanates - island silicates (nesosilicates)
System no. to Strunz
and to Dana
9.AC.15 ( 8th edition : VIII / A.06)
03/01/01/01
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  = 8.11 (synthetic 8.17 ÅÅ
Formula units Z  = 8
Physical Properties
Mohs hardness Please complete!
Density (g / cm 3 ) calculated: 3.90
Cleavage Please complete!
colour colorless, violet, bluish, smoky gray
Line color Please complete!
transparency Please complete!
shine Please complete!
Crystal optics
Refractive index n  = 1.768
Birefringence none, as it is optically isotropic

Ringwoodite is the high pressure - modification of olivine and a rarely occurring at the surface mineral from the mineral class of "silicates and Germanates". It crystallizes in the cubic crystal system with the idealized chemical composition of Mg 2 (SiO 4 ) is thus a magnesium - silicate . Structurally, ringwoodite belongs to the island silicates as well as to the supergroup of spinels with the formula notation SiMg 2 O 4 standardized for spinels .

Due to the formation of mixed crystals between the minerals of the oliving group, the formula for ringwoodite is often given as a mixed formula with (Mg, Fe) 2 [SiO 4 ]. In nature, Mg-rich mixed crystals predominate; γ-Fe 2 (SiO 4 ) was only recently detected in natural samples and has therefore been called ahrensite since 2013 .

Ringwoodite is translucent and so far could only be found in the form of rounded grains up to about 100  micrometers in size and massive mineral aggregates . In its pure form, Ringwoodite is colorless. However , it can also take on a violet, bluish or smoky gray color through foreign admixtures.

Etymology and history

Ringwoodite was first discovered in mineral samples of the " Tenham meteorite ", which fell in 1879 near South Gregory in the Australian state of Queensland . The mineral was described in 1969 by RA Binns, RJ Davis and SJB Reed, who named the mineral after the Australian experimental geophysicist and geochemist Alfred Edward Ringwood (1930-1993).

The iron-containing analogue of ringwoodite, ahrensite, was named in 2013 after the American mineral physicist Thomas J. Ahrens (1936-2010).

classification

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

In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , the ringwoodite belonged to the mineral class of "silicates and germanates" and there to the department of "island silicates (nesosilicates)", where together with wadsleyite it belongs to the unnamed group VIII / A. 06 made.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the IMA, also classifies ringwoodite in the category of "island silicates (nesosilicates)". However, this is further subdivided according to the possible presence of further anions and the coordination of the cations involved , so that the mineral is classified in the sub-section “Island silicates without additional anions; Cations in octahedral [6] he coordination ”can be found, where it forms the unnamed group 9.AC.15 as the only member .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns ringwoodite to the class of "silicates and Germanates" and there in the department of "island silicate minerals ". Here he is to be found as the only member in the unnamed group 51.03.03 within the sub-section “ Island silicates: SiO 4 groups with all cations only in octahedral [6] coordination”.

Crystal structure

Ringwoodite crystallizes cubically in the space group Fd 3 m (space group no. 227) with the lattice parameter a  = 8.11  Å (in synthetic, chemically pure form 8.17 Å) and 8 formula units per unit cell . The crystal lattice has the structure of spinel , which is why ringwoodite or γ-olivine is sometimes referred to as "spinel", especially in geophysical literature. Template: room group / 227

Molar volume of ringwoodite (γ-Mg2SiO4) as a function of pressure at room temperature Molar volume of ahrensite (γ-Fe2SiO4) as a function of pressure at room temperature
Molar volume of ringwoodite (γ-Mg 2 SiO 4 ) as a function of the pressure at room temperature
Molar volume of ahrensite (γ-Fe 2 SiO 4 ) as a function of pressure at room temperature

Modifications and varieties

The compound Mg 2 (SiO 4 ) is trimorphic and occurs naturally in addition to the cubic ringwoodite as orthorhombically crystallizing forsterite and also as orthorhombic, but in a different space group crystallizing wadsleyite .

Education and Locations

Thin section of a common chondrite from northwest Africa with shock vein and ringwoodite

As a high pressure - modification of Olivinminerals forsterite ringwoodite is in the mantle from about a depth of 520 km ( 520 km discontinuity ) stable. In stone meteorites ( chondrites ), on the other hand, the mineral is formed by impact metamorphosis ( shock wave metamorphosis ) when the material is strongly compressed during impact and exposed to high pressures and temperatures. The occurrence of ringwoodite is one of several indicators for shock level S6 according to the Stöffler-Keil-Scott scale. In the event of even stronger shock events, the meteorite is largely melted and an impact melt forms, after which high pressure phases can no longer be detected after solidification.

In the Tenham meteorite, ringwoodite was found in small veins that cut through the base mass of the meteorite, which were formed by the brecciation when the meteorite impacted. As accompanying minerals were found majorite , magnesium-containing silicate glass and also the first time discovered in Enham meteorite minerals Akimotoit and Bridgmanit . The Chondrite Coorara , which also fell in Australia near Rawlinna in Western Australia in 1966 , also contained ringwoodite and majorite (magnesium-iron garnet ).

Other previously known sites where meteorites with ringwoodite fell include the Grove Mountains on the American highlands in Antarctica, Pampa del Infierno in the Argentine department of Almirante Brown , Sui and Gaogang in China, the Peace River and Catherwood ( Saskatchewan Province ) in Canada, Munizip al-Jabal al-Gharbi in Libya, Dhofar in Oman and several counties in New Mexico and Umbarger in Randall County in the United States of America.

In China, ringwoodite was also found in a basalt field near Hannuoba in Wanquan County (Hebei).

Diamond with enclosed ringwoodite

During investigations on a Brazilian find, jacket material with ringwoodite as an inclusion within a diamond was found. Investigations in the USA corroborated the hypothesis that the earth's mantle could contain large amounts of hydroxide contained in ringwoodite .

See also

literature

  • RA Binns, RJ Davis, SJB Reed: Ringwoodite, natural (Mg, Fe) 2 SiO 4 spinel in the Tenham meteorite . In: Nature . tape 221 , March 8, 1969, p. 943-944 , doi : 10.1038 / 221943a0 .
  • Michael Fleischer : New mineral names. Ringwoodite . In: American Mineralogist . tape 54 , 1969, p. 1218–1223 ( rruff.info [PDF; 379 kB ; accessed on January 3, 2017]).
  • LC Coleman: Ringwoodite and majorite in the Catherwood meteorite . In: The Canadian Mineralogist . tape 15 , 1977, pp. 97–101 ( rruff.info [PDF; 772 kB ; accessed on January 3, 2017]).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 665 (first edition: 1891).

Web links

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

Individual evidence

  1. a b Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: March 2019. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, March 2019, accessed June 16, 2019 .
  2. ^ A b c 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.  539 .
  3. 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 c Malcolm Back, William D. Birch, Hans-Peter Bojar and others: The New IMA List of Minerals - A Work in Progress - Updated: January 2014. (PDF 1602 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, March 2019, accessed June 16, 2019 .
  5. a b WH Baur: Computer-simulated crystal structures of observed and hypothetical Mg 2 SiO 4 . In: American Mineralogist . tape 57 , 1972, p. 709-731 ( arizona.edu [TXT; accessed January 3, 2017]).
  6. Ringwoodite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 64  kB ; accessed on January 3, 2017]).
  7. Ringwoodite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 16, 2019 .
  8. Ferdinando Bosi, Cristian Biagioni, Marco Pasero: Nomenclature and classification of the spinel supergroup . In: European Journal of Mineralogy . tape 31 , no. 1 , September 12, 2018, p. 183–192 , doi : 10.1127 / ejm / 2019 / 0031-2788 (English).
  9. OR Norton: The Cambridge Encyclopedia of Meteorites . Cambridge University Press, Cambridge 2002, ISBN 0-521-62143-7 , pp. 93-95 .
  10. List of localities for ringwoodite in the Mineralienatlas and Mindat
  11. Mindat - Hannuoba basalt field, Wanquan Co., Zhangjiakou Prefecture, Hebei Province, China (source: Hongsen Xie, Huifen Zhang, Yueming Zhang, Huigang Xu, Shijie Zhuang: High-pressure hydrous mineral association in Hannuoba lherzolite . In: Acta Mineralogica Sinica . band  4 , no. 4 , 1984, pp. 289-295 , doi : 10.1007 / BF02864872 . )
  12. Mineral water in the earth's core is based on: Hydrous mantle transition zone indicated by ringwoodite included within diamond
  13. Wissenschaft.de: confirmed water in the earth's mantle