Greigite
- IMA 1963-007
Greigite is a rarely occurring mineral from the mineral class of sulfides and sulfosalts. It crystallizes in a cubic crystal system having a chemical composition FeII ( FeIII) 2S4 and intergrown forms spheres octahedron with rounded corners of up to 0.5 mm size. Rarely, cubic crystals, granules and fine powders are found. The mineral is of pale pink, metallic - blue -starting color; in feinkornigem state also black, polished surfaces are creamy white.
Greigite forms a mineral series Violarit, wherein the trivalent iron is replaced with nickel. The mineral is the sulfur analogue of the magnetite.
Special Features
How Magnetite is strongly magnetic greigite. This magnetism also causes aggregation of smaller greigite grains to form larger aggregates.
Thermally the mineral up to 282 ° C is stable. On heating the mineral at temperatures above 282 ° C in a closed vial, it turns into pyrrhotite ( Fe 0 .85 -1S ), at higher temperatures also pyrite FeS2 to.
Greigite only dissolves slowly in hydrofluoric acid and hydrochloric acid.
Etymology and history
Various magnetic, spinel-type iron sulfides were predicted by various authors since 1958 and artificially synthesized in the laboratory. The mineral was first discovered in 1964 by Brian J. Skinner, Richard C. Erd and Frank S. Grimaldi in the type locality Kramers- Four Corners area in San Bernardino County in the U.S. state of California. They named the new mineral after the American mineralogist and physical chemist Joseph Wilson Greig ( 1895-1977 ).
Classification
In the classification by Strunz greigite is classified in the sulfides and sulfosalts. In the 8th edition he made with Bornhardtit, Cadmoindit, Carrollite, Daubréelith, Fletcherit, Florensovit, Indit, Kalininit, linnaeite, Polydymit, Siegenit, Trüstedtit, Tyrrellit and Violarit the Linneitgruppe that of metal sulfides with a ratio of metal to sulfur < 1:1 belongs. In the 9th edition of the sulfides are divided in more detail, here is one of greigite with Bornhardtit, Cadmoindit, Carrollite, Cuproiridsit, Cuprorhodsit, Daubréelith, Ferrorhodsit, Fletcherit, Florensovit, Indit, Kalininit, linnaeite, Malanit, Polydymit, Siegenit, Trüstedtit, Tyrrellit, Violarit Xingzhongit and a lower group of metal sulfides with a ratio of M: S of 3:4.
In the scheme of minerals by Dana greigite is a member of Linneitgruppe, a subgroup of the sulfides, selenides and tellurides with the composition AmBn Xp, with (m n): p = 3:4 (A, B: Metals, X: sulfur)
Education and Locations
Greigite forms in sediments of water bodies. Responsible for the formation of one hand, sulfate-reducing bacteria such as Desulfovibrio desulfuricans, which reduce sulfate to sulfide under anaerobic and alkaline conditions. On the other hand Greigitkristalle are formed in the cells of magnetotactic bacteria that align with the aid of a arranged in a row in the geomagnetic field Greigitkristallen.
Greigite is associated with montmorillonite minerals of chlorite, calcite, colemanite and Veatchite in the type locality or sphalerite, pyrite, marcasite, galena, calcite and dolomite at a different location in Zacatecas in Mexico.
Other Locations in addition to the type locality are among others in Boron and Orick in California, Zacatecas, Mexico, in the Black Sea, Montemesola in Italy, Lojane in Macedonia, St. Teath in Cornwall, United Kingdom and Ōdate in Japan.
Crystal structure
Greigite crystallizes in the cubic crystal system in space group Fd3m with lattice parameters a = 9.876 Å and eight formula units per unit cell. The structure corresponds to a spinel structure is substituted with sulfur in the oxygen ( Thiospinell ).