Stishovite

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 of SiO2 and is only microcrystalline, colorless aggregates.

Etymology and history

Stishovite was named after the Russian crystallographer Sergei Stischow (* 1937), which in 1961 together with SW Popova for the first time succeeded in producing the hitherto theoretical modification known as synthetic.

1962 stishovite was then discovered in nature in the Barringer Crater, a meteorite crater in the U.S. state of Arizona and has since been recognized by the International Mineralogical Association (IMA ) as a mineral. Stishovite also served to demonstrate that the Ries is an impact crater.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the stishovite belonged to the mineral class of " oxides and hydroxides " and then to the Department of " oxides with the molar ratio of metal: oxygen = 1: 2 ," where he, together with coesite, cristobalite, melanophlogite, Moganite, opal, quartz and tridymite, the " quartz group " with the system no. IV/D.01 formed.

The 9th edition used since 2001, valid and of the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the stishovite also in the class of " oxides and hydroxides " and there in the department of " oxides with the molar ratio of metal: oxygen = 1: 2 and comparable " one. This division, however, is further divided according to the relative size of the cations involved and of belonging to a larger mineral family or the crystal structure, so that the mineral "With small cations: Silica family " according to the directorate is to find where it only together with cristobalite forms the unnamed group 4.DA.15.

The mainly common in English-speaking classification of minerals according to Dana assigns the stishovite in the class of " oxides and hydroxides " and there in the department of " oxides ". Here he is with rutile, Ilmenorutil, Struverit, pyrolusite, cassiterite, Plattnerit, Argutit and Squawcreekit in the " Rutilgruppe ( Tetragonal: P4/mnm ) " with the system no. 04:04:01 to find within the sub-division of "simple oxides with a cation charge of 4 ( AO2 ) ".

Modifications and varieties

Stishovite Coesite besides a high-pressure polymorph of silica quartz (including gravure or α - quartz).

Further modifications are cristobalite and tridymite as high-temperature modifications, Lechatelierite as amorphous silica glass, which is, however, not recognized by the IMA as a mineral and also amorphous, hydrous opal.

Education and Locations

Stishovite arises as a high-pressure mineral typically at a meteorite impact (Impact) and is adjacent coesite and diaplektischen glasses in suevite, an impact - rock, contain.

Other localities are adjacent to the Barringer Crater and the Ries including the Zagami Mars meteorite in Nigeria, the Muonionalusta meteorite in Sweden, the Vredefort Crater in South Africa, as well as in various meteorite craters in the USA.

Crystal structure

Stishovite crystallized tetragonal in the space group P42/mnm ( Raumgruppen-Nr. 136) with the lattice parameters a = 4.18 Å and c = 2.66 Å and two formula units per unit cell.

In contrast to the low-pressure modification of the quartz Stishovite the silicon is bound six times, so that the mineral has a much more compact structure. This is also evident in the comparison of densities. Quartz has a density of 2.65 g/cm3 and 4.32 g/cm3 of stishovite.

Stishovite (GPa ) is stable at room temperature pressing 8 Gigapascal and goes at about fifty GPa in the related orthorhombic crystal structure of type II stishovite. At atmospheric pressure, stishovite is metastable.