Evidence of biogenic greigite (ferrimagnetic Fe3S4) in soil |
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| Authors: | H STANJEK J W E FASSBINDER H VALI H WÄGELE W GRAF |
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| Institution: | Lehrstuhl für Bodenkunde der Technischen Universität München, Hohenbachernstraβe, 85350 Freising-Weihenstephan, Germany;Bayerisches Landesamt für Denkmalpflege Abt. Bodendenkmalpflege Archäol. Prospektion und Luftbildarchäologie, Hofgraben 4, 80539 München, Germany;Department of Geological Sciences, McGill University, 3450 University Street, Montreal, Quebec, Canada H3A 2A7;Zooökologie, Fachhereich 7 Universität Oldenburg, Postfach 2503, 26131 Oldenburg, Germany;Institut für Hydrologie Gesellschaft für Strahlenforschung, Ingolstädter Landstraβe 1, 80807 Neuherberg, Germany |
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| Abstract: | The occurrence of greigite (Fe3S4) in soils is reported for the first time. It forms irregularly-shaped aggregations within plant cells in the Gr2 horizon of a gley soil developed from colluvial material. Greigite was identified by X-ray diffraction and magnetic measurements and was investigated by optical and transmission electron microscopy. Biogenic formation is proposed, based on the elongated shape of single greigite crystals, and sulphur isotope analyses, which showed a depletion in 34S relative to the soil-water sulphate. The cell-edge length of 0.98639±0.00003 nm is significantly smaller than values reported for sedimentary greigite. The mean coherence length of 27 nm agrees with TEM observations and indicates that the single greigite crystals lie in the superparamagnetic region. However, the fine aggregates show magnetically single-domain behaviour. Greigite is the only carrier of a stable magnetic remanence in the soil profile studied. |
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