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

• Published in: Geochimica et cosmochimica acta 1997-03, Vol.61 (5), p.1107-1111
• Main Authors: Trolard, F., Génin, J.-M.R., Abdelmoula, M., Bourrié, G., Humbert, B., Herbillon, A.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Chemical Sciences
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/S0016-7037(96)00381-X

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.