IRON LOCAL STRUCTURE IN TEKTITES AND IMPACT GLASSES BY EXTENDED X-RAY ABSORPTION FINE STRUCTURE AND HIGH-RESOLUTION X-RAY ABSORPTION NEAR-EDGE STRUCTURE SPECTROSCOPY
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dc.contributor.author | Giuli G. | |
dc.contributor.author | Pratesi G. | |
dc.contributor.author | Cipriani C. | |
dc.contributor.author | Paris E. | |
dc.date.accessioned | 2021-09-18T04:59:41Z | |
dc.date.available | 2021-09-18T04:59:41Z | |
dc.date.issued | 2002 | |
dc.identifier | https://elibrary.ru/item.asp?id=1324568 | |
dc.identifier.citation | Geochimica et Cosmochimica Acta, 2002, 66, 24, 4347-4353 | |
dc.identifier.issn | 0016-7037 | |
dc.identifier.uri | https://repository.geologyscience.ru/handle/123456789/30318 | |
dc.description.abstract | The local structure of iron in three tektites has been studied by means of Fe K-edge extended X-ray absorption fine structure (EXAFS) and high-resolution X-ray absorption near-edge structure (XANES) spectroscopy in order to provide quantitative data on <fe-o> distance and Fe coordination number. The samples studied are a moldavite and two australasian tektites. Fe model compounds with known Fe oxidation state and coordination number were used as standards in order to extract structural information from the XANES pre-edge peak. EXAFS-derived grand mean <fe-o> distances and Fe coordination numbers for the three tektite samples are constant within the estimated error (<fe-o > =2.00 Α +/- 0.02 Α, CN = 4.0 +/- 0.4). In contrast to other data from the literature on Fe-bearing silicate glasses, the tektites spectra could not be fitted with a single Fe-O distance, but rather were fit with two independent distances (2 x 1.92 Α and 2 x 2.08 Α). High-resolution XANES spectra of the three tektites display a pre-edge peak whose intensity is intermediate between those of staurolite and grandidierite, thus suggesting a mean coordination number intermediate between 4 and 5. Combining the EXAFS and XANES data for Fe, we infer the mean coordination number to be close to 4.5.Comparison of the tektites XANES spectra with those of a suite of different impact glasses clearly shows that tektites display a relatively narrow range of Fe oxidation state and coordination numbers, whereas impact glasses data span a much wider range of Fe oxidation states (from divalent to trivalent) and coordination numbers (from tetra-coordinated to esa-coordinated). These data suggest that the tektite production process is very similar for all the known strewn fields, whereas impact glasses can experience a wide variety of different temperature-pressure-oxygen fugacity conditions, leading to different Fe local structure in the resulting glasses. These data could be of aid in discriminating between tektite-like impact glasses and impact glasses sensu strictu. | |
dc.title | IRON LOCAL STRUCTURE IN TEKTITES AND IMPACT GLASSES BY EXTENDED X-RAY ABSORPTION FINE STRUCTURE AND HIGH-RESOLUTION X-RAY ABSORPTION NEAR-EDGE STRUCTURE SPECTROSCOPY | |
dc.type | Статья |
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