HR: 1400h
AN: V23B-06    [Abstracts]
TI: Speciation of Iron in Silicic Glasses: Inferences From Spectroscopic Methods and TEM
AU: * Galoisy, L
EM: galoisy@impmc.jussieu.fr
AF: Insitut of Mineralogy and Physics of condensed Matter (IMPMC), 140 rue de Lourmel, Paris, 75015, France
AU: Calas, G
EM: calas@impmc.jussieu.fr
AF: Insitut of Mineralogy and Physics of condensed Matter (IMPMC), 140 rue de Lourmel, Paris, 75015, France
AU: Menguy, N
EM: menguy@impmc.jussieu.fr
AF: Insitut of Mineralogy and Physics of condensed Matter (IMPMC), 140 rue de Lourmel, Paris, 75015, France
AB: Iron environment in silicic glasses has been investigated using optical absorption spectroscopy (OAS), X-ray Absorption Near Edge Structure (XANES), Electron Paramagnetic Resonance (EPR) and TEM. The samples are calco-alkaline silicic glasses from different localities and containing 0.5 to 2 wt% Fe. The redox state of iron in silicate glasses and the local environment around Fe2+ and Fe3+ is known to influence properties such as color or viscosity and crystal-liquid element partitioning, for glasses and melts, respectively. Considering eruption conditions, this information can give a better understanding of the cooling conditions and setting of lava flows. The spectra of silicic glasses are strongly different from that of synthetic glasses and tektites. All spectroscopic methods show the presence of Fe3+ and Fe2+ cations belonging to the glassy network associated with clustered superparamagnetic Fe-oxides. TEM data indicate that nanometric Fe-oxide clusters are poorly crystallized. The spectroscopic data on obsidians have been compared to those recorded on magnetite and synthetic glasses to assess the importance of Fe oxide clusters. These clusters are responsible for the variety of coloration of these obsidians. The speciation of iron in these glasses and associated clusters will be discussed in terms of formation conditions.
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3640 Igneous petrology
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly