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| Titel |
Fe K-edge XANES and pre-edge polarization dependance for the determination of the oxidation state of iron in antigorite and other phyllosilicates |
| VerfasserIn |
M. Munoz, O. Vidal, C. Marcaillou, S. Pascarelli, O. Mathon, F. Farges |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063317
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| Zusammenfassung |
| Iron oxidation state in minerals is often a crucial indicator for the understanding of
mineralogical reactions related to hydrothermalism, or various natural processes. We
investigated here the influence of the linear polarization of the synchrotron X-ray beam on the
determination of the iron oxidation state in phyllosilicates. Fe K-edge XANES spectra and
pre-peaks of biotite (Bt), chlorite (Chl), talc (Tlc) and antigorite (Atg) crystals have been
recorded at different crystal orientations. As a function of the crystal orientation, the
experimental results show, 1) important changes both for XANES and pre-peaks, 2) typical
changes of spectral signatures for all mineral species, 3) uncorrelated changes between
XANES and pre-peaks, 4) important changes of the pre-peak energies, but no significant
change of the integrated areas. Ab initio XANES calculations, performed for 6
orientations of the Bt structure are consistent with the experimental measurements.
The energy position of the pre-peak centroids changes with crystal orientation by
0.4Â eV for Bt and Tlc crystals, and by 0.2Â eV for Chl and Atg, which correspond to
XFe(apparent)3+ variations (2δ) of 0.22 and 0.15, respectively. Measurements on
powdered crystals show that – (2/3)2δ |
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