Stishovite
| Stishovite | |
|---|---|
| General and classification | |
| chemical formula | SiO 2 |
|
Mineral class (and possibly department) |
Oxides / hydroxides - oxides with metal: oxygen = 1: 2 |
|
System no. to Strunz and to Dana |
4.DA.40 ( 8th edition : IV / D.01) 04.04.01.09 |
| Crystallographic Data | |
| Crystal system | tetragonal |
| Crystal class ; symbol | ditetragonal-dipyramidal 4 / m 2 / m 2 / m |
| Room group (no.) | P 4 2 / mnm (No. 136) |
| Lattice parameters | a = 4.18 Å ; c = 2.66 Å |
| Formula units | Z = 2 |
| Physical Properties | |
| Mohs hardness | 8.5 to 9 |
| Density (g / cm 3 ) | 4.29 to 4.35 |
| Cleavage | not defined |
| Break ; Tenacity | not defined |
| colour | colorless |
| Line color | White |
| transparency | transparent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n ω = 1.799 n ε = 1.826 |
| Birefringence | δ = 0.027 |
| Optical character | uniaxial positive |
Stishovite ( Russian стишовит ) is a rarely occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the tetragonal crystal system with the chemical composition SiO 2 and develops exclusively micro- crystalline , colorless aggregates .
Etymology and history
Stishovite was named after the Russian crystallographer Sergei Stischow (* 1937), who, together with SW Popowa, succeeded for the first time in 1961 in synthetically producing the previously only theoretically known modification. It was predicted in 1952 by Albert Francis Birch .
In 1962, stishovite was discovered in nature in the Barringer Crater , a meteorite crater in the US state of Arizona by Edward CT Chao and has since been recognized as a mineral by the International Mineralogical Association (IMA). Stishovite also served to prove that the Nördlinger Ries is an impact crater .
classification
In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the stishovite belonged to the mineral class of "oxides and hydroxides" and there to the department of "oxides with the molar ratio metal: oxygen = 1: 2", where it was used together with Coesite , Cristobalite , melanophlogite , mogánite , opal , quartz and tridymite the "quartz group" with the system no. IV / D.01 .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns stishovite to the class of "oxides and hydroxides" and there into the department of "oxides with the molar ratio of metal: oxygen = 1: 2 and comparable “. However, this section is further subdivided according to the relative size of the cations involved as well as belonging to a larger mineral family or the crystal structure, so that the mineral can be found in the sub-section “With small cations: Silica family”, where it is only together with cristobalite forms the unnamed group 4.DA.15 .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns stishovite to the class of "oxides and hydroxides" and there in the "oxides" category. Here it is together with rutile , ilmenorutile , struverite , pyrolusite , cassiterite , plattnerite , argutite and squawcreekite in the "rutile group (tetragonal: P 4 / mnm )" with the system no. 04:04:01 within the subdivision of the " Simple oxides having a cationic charge of 4 + (AO 2 ) to find."
Modifications and varieties
Stishovite is next Coesite a high pressure - modification of the silica quartz (also gravure or α-quartz).
Further modifications are cristobalite and tridymite as high-temperature modifications, lechatelierite as amorphous silica glass , which is not recognized as a mineral by the IMA, and the likewise amorphous, water-containing opal.
Education and Locations
Stishovite produced as high pressure Mineral typically at a meteorite (Impact) and is adjacent to and Coesite diaplektischen glasses in Suevite , a Impakt- rock containing.
Other localities are in addition to the Meteor Crater and the Ries including the Zagami - Mars meteorite in Nigeria , the Muonionalusta meteorite in Sweden , the Vredefort crater in South Africa , and in various meteorite craters in the United States .
Crystal structure
Stishovite crystallizes tetragonally in the space group P 4 2 / mnm (space group no. 136) with the lattice parameters a = 4.18 Å and c = 2.66 Å as well as 2 formula units per unit cell .
In contrast to the low-pressure modifications of quartz , in stishovite the silicon is bound sixfold, which means that the mineral has a much more compact structure. This is also clear when comparing the densities . Quartz has a density of 2.65 g / cm 3 and stishovite of 4.32 g / cm 3 .
Stishovite is stable at room temperature from a pressure of 8 gigapascals (GPa) and changes to the related orthorhombic crystal structure of the Stishovite II type at fifty GPa. Stishovite is metastable at normal pressure .
See also
literature
- SM Stischow, SW Popowa: Новая плотная модификация кремнезёма . In: Геохимия , 1961: 10, pp. 837–839
- Martin Okrusch, Siegfried Matthes: Mineralogy . 7th edition. Springer Verlag, Berlin 2005, ISBN 3-540-23812-3
- Stefan Weiß: The large Lapis mineral directory . 4th edition. Christian Weise Verlag, Munich 2002, ISBN 3-921656-17-6
Web links
- Mineral Atlas: Stishovite (Wiki)
- Webmineral - stishovite (Engl.)
- MinDat - Stishovite (Eng.)
- Handbook of mineralogy - stishovite (PDF; 66 kB)
Individual evidence
- ^ A b c Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 206 .
- ^ "High-pressure crystal chemistry of stihovite", NL Ross et al., American Mineralogist, Vol 75, pp 739-747, 1990 (PDF; 1.1 MB)