Identification of a green rust mineral in a reductomorphic soil by Mossbauer and Raman spectroscopies

Abstract : Mössbauer and Raman spectroscopies are used to identify for the first time a green rust as a mineral in a reductomorphic soil from samples extracted in the forest of Fougères (Brittany-France). The Mossbauer spectrum displays two characteristic ferrous and ferric quadrupole doublets, the abundance ratio Fe(II)/Fe(Ill) of which is close to 1. Comparison with synthetic mixed valence Fe(II)Fe(HI) hydroxides supports the conclusion that the most probable formula is Fe2(OH)5, i.e., according to the pyroaurite-like crystal structure [Fe(n1Fe1III)(OH),]+o [OH] -. The microprobe Raman spectrum exhibits two bands at 518 and 427 cm-' as for synthetic green rusts. When exposed to the air, the new mineral goes rapidly from bluish-green to ochrous. The formula is compatible with the values of ionic activity products Q for equilibria between aqueous iron species and minerals obtained from soil waters, which suggests that this new mineral is likely to control the mobility of Fe in the environment.
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F. Trolard, J.-M.R. Génin, Mustapha Abdelmoula, G. BourriÉ, B. Humbert, et al.. Identification of a green rust mineral in a reductomorphic soil by Mossbauer and Raman spectroscopies. Geochimica et Cosmochimica Acta, Elsevier, 1997, 61 (5), pp.1107-1111. ⟨10.1016/S0016-7037(96)00381-X⟩. ⟨hal-01944243⟩

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