Greigite

Greigite is an iron sulfide mineral with formula Fe3S4. Like the related oxide magnetite (Fe₃O₄), greigite is magnetic. It is a mixed-valence compound, featuring both Fe(II) and Fe(III) centers in a 1:2 ratio. Both metal sites, which conform to the thiospinel motif, are high spin. Greigite occurs as microscopic (< 0.03 mm) isometric hexoctahedral crystals and as minute sooty masses. It is a bio-mineral produced by and found in magnetotactic bacteria. It is a pale pink to metallic blue-black mineral with a specific gravity of 4.049 g/cm3 and a Mohs hardness of 4 to 4.5.[1][2][3]

It occurs in lacustrine sediments with clays, silts and arkosic sand often in varved sulfide rich clays. It also in hydrothermal veins. It is formed by magnetotactic bacteria and sulfate-reducing bacteria.[2]

Association minerals include montmorillonite, chlorite, calcite, colemanite, veatchite, sphalerite, pyrite, marcasite, galena and dolomite.[2]

It was first described in 1964 for an occurrence in San Bernardino County, California, and named for the mineralogist and physical chemist Joseph W. Greig (1895-1977).[4]

References

1. ^ Vaughan, D. J.; Craig, J. R. “Mineral Chemistry of Metal Sulfides" Cambridge University Press, Cambridge: 1978. ISBN 0521214890.
2. ^ a b c http://rruff.geo.arizona.edu/doclib/hom/greigite.pdf Mineral Data
3. ^ http://www.mindat.org/min-1747.html Mindat with location data
4. ^ http://webmineral.com/data/Greigite.shtml Webmineral data

List of minerals