GEOC 156 |
| Bruno Lanson1, Alain Manceau1, Mario Villalobos2, Brandy Toner3, and Garrison Sposito3. (1) Environmental Geochemistry Group, CNRS / University of Grenoble, LGIT, Maison des Géosciences, Grenoble cedex 9, 38041, France, (2) Environmental Bio-Geochemistry Group, Instituto de Geografía, UNAM, LAFQA, National Autonomous University of Mexico (UNAM), CU México 04510, Mexico, (3) Division of Ecosystem Sciences, UC Berkeley, 235 Hilgard Hall, Berkeley, CA 94720-3110 |
| The high proportion of structural defects commonly reported in layered minerals such as phyllomanganates strongly reduces the efficiency of structure refinement methods. One effective way to determine the actual structure of defective systems is the calculation of XRD patterns using the formalism described by Drits and Tchoubar (1990). This procedure proved successful to determine the structure of different birnessites. In some phyllomanganates, the abundance of random stacking faults leads to structures without three-dimensional ordering (turbostratic stacking). Even in these most defective structures, X-ray diffractograms exhibit noticeable modulations of the 20,11 and 31,02 scattering bands. These modulations provide relevant structural information, which includes unit-cell parameters, and atomic coordinates and occupancies of the different sites. In particular, these modulations vary as a function of the amount of vacant layer sites capped by interlayer Mn cations. The usefulness of this approach is illustrated with the biogenic phyllomanganate produced in vitro by Pseudomonas putida, and with other samples obtained from permanganate reduction. |
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Microbially Mediated Manganese and Iron Oxidation in the Biosphere
1:45 PM-6:20 PM, Wednesday, March 31, 2004 Marriott -- Marquis NE, Oral
Division of Geochemistry |