Greigit
| Greigit | |
|---|---|
| General and classification | |
| other names |
IMA 1963-007 |
| chemical formula |
|
|
Mineral class (and possibly department) |
Sulfides and sulfosalts |
|
System no. to Strunz and to Dana |
2.DA.05 ( 8th edition : II / D.01) 02.10.01.10 |
| Crystallographic Data | |
| Crystal system | cubic |
| Crystal class ; symbol | -3m |
| Space group | Fd 3 m (No. 227) |
| Lattice parameters | a = 9.88 Å |
| Formula units | Z = 8 |
| Physical Properties | |
| Mohs hardness | 4 to 4.5 |
| Density (g / cm 3 ) | measured: 4.049; calculated: 4.079 |
| Cleavage | Please complete |
| colour | light pink, tapering to metallic blue |
| Line color | black |
| transparency | opaque (opaque) |
| shine | Metallic luster |
| magnetism | strong magnetic |
Greigit is a rarely occurring mineral from the mineral class of sulfides and sulfosalts with the chemical composition Fe 2+ Fe 3+ 2 S 4 and is therefore a special form of iron sulfide that contains iron in two different oxidation states .
Greigit crystallizes in the cubic crystal system and forms spheres of fused octahedra with rounded corners of up to 0.5 millimeters in size. Cubic crystals, grains and fine-grained powders are also rarely found. Freshly taken samples are light pink in color; in the air the mineral turns metallic blue after a while. In a fine-grained state, Greigit can also be black, whereas polished surfaces appear creamy white.
Greigit forms a mineral series with violarite , in which the trivalent iron is replaced by nickel . The mineral is the sulfur analogue to magnetite .
Etymology and history
Various magnetic, spinel-like iron sulfides have been predicted by various authors since 1958 and synthesized artificially 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 , California . They named the new mineral after the American mineralogist and physical chemist Joseph Wilson Greig (1895–1977).
classification
In the Strunz system , Greigit is classified under sulfides and sulfosalts. In the 8th edition he formed with Bornhardtit , Cadmoindit , Carrollit , daubréelite , Fletcherit , Florensovit , Indit , Kalininit , linnaeite , Polydymit , Siegenit , Trüstedtit , Tyrrellit and Violarite the Linneitgruppe that the metal sulfides with a ratio of metal to sulfur of <1: 1 heard. In the 9th edition , the sulfides are divided precisely, here greigite counts with Bornhardtit, Cadmoindit, Carrollit, Cuproiridsit , Cuprorhodsit , daubréelite, Ferrorhodsit , Fletcherit, Florensovit, Indit, Kalininit, linneite, Malanit , Polydymit, Siegenit, Trüstedtit, Tyrrellit, Violarite and xingzhongite to a subgroup of the metal sulfides with an M: S ratio of 3: 4.
In the systematics of minerals according to Dana , Greigit is a member of the Linneit group, a subgroup of sulfides, selenides and tellurides with the composition Am Bn Xp, with (m + n): p = 3: 4 (A, B: metals, X: Sulfur).
Crystal structure
Greigit crystallizes in the cubic crystal system in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 9.88 Å and eight formula units per unit cell . The structure corresponds to a spinel structure in which oxygen is replaced by sulfur (thiospinel).
properties
Like magnetite, greigite is strongly magnetic . This magnetism also causes smaller Greigit grains to clump together to form larger aggregates.
The mineral is thermally stable up to 282 ° C. When the mineral is heated to temperatures above 282 ° C in a closed ampoule, it is converted into pyrrhotite (Fe 0.85-1 S), and at higher temperatures also into pyrite FeS 2 .
Greigit only dissolves slowly in hydrofluoric and hydrochloric acid .
Education and Locations
Greigit forms in sediments of water. On the one hand, sulfate-reducing bacteria such as Desulfovibrio desulfuricans , which reduce sulfate to sulfide under anaerobic and neutral to alkaline conditions, are responsible for the formation . On the other hand, greigite crystals are formed in the cells of magnetotactic bacteria, which align with the help of a row of greigite crystals in the earth's magnetic field.
Greigite is associated with montmorillonite , minerals of the chlorite group , calcite , colemanite and veatchite in the type locality or sphalerite , pyrite, marcasite , galena , calcite and dolomite at another location in Zacatecas in Mexico .
Other sites in addition to the type locality include Boron and Orick in California, Zacatecas in Mexico, in the Black Sea , Montemesola in Italy , Lojane in Macedonia , St. Teath in Cornwall , United Kingdom and Ōdate in Japan .
See also
literature
- Brian J. Skinner, Richard C. Erd, and Frank S. Grimaldi: Greigite, the thio-spinel of iron; a new mineral . In: American Mineralogist . tape 49 , no. 5 , 1964, pp. 543–555 ( minsocam.org [PDF; 818 kB ; accessed on March 30, 2018]).
Web links
Individual evidence
- ↑ a b c d e f Greigite . 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; 62 kB ; accessed on March 30, 2018]).
- ^ A b 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. 93 .
- ↑ Mindat - Greigite-Violarite Series (English)
- ↑ a b c d e Brian J. Skinner, Richard C. Erd and Frank S. Grimaldi: Greigite, the thio-spinel of iron; a new mineral . In: American Mineralogist. 1964, 49, 5, pp. 543-555.
- ↑ Bruce M. Moskowitz: Biomineralization of magnetic minerals , In: US National Report to IUGG, 1991-1994, Rev. Geophys. , Vol. 33 Suppl., American Geophysical Union 1995.