Characterization of cation oxidation states in geologic materials
| Autor: | Anne V. McGuire, M. Darby Dyar |
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| Rok vydání: | 1992 |
| Předmět: | |
| Zdroj: | Proceedings, annual meeting, Electron Microscopy Society of America. 50:1742-1743 |
| ISSN: | 2690-1315 0424-8201 |
| DOI: | 10.1017/s0424820100133345 |
| Popis: | One shortfall of electron microprobe analysis is the inability of x-ray spectroscopic methods to distinguish multiple valence states of atoms. In geologic materials, many elements (eg. Fe, Ti, Cr, Mn, Cu, Eu) may exhibit multiple valence states and their quantitative analysis can be important in solving geologic problems. For instance, Fe2+/Fe3+ ratios in minerals may be useful in determining the oxygen fugacities in which rocks equilibrated. In the past, wet chemical methods were generally used to analyze mineral compositions and Fe2+/Fe3+ ratios were routinely determined. The advent of electron microprobe analysis was accompanied by a decrease in determination of iron oxidation states. The modern microprobe analyst generally deals with the inability to measure Fe2+/Fe3+ ratios by picking one of several assumptions: (a) treat all iron as Fe2+; (b) treat all iron as Fe3+; or (c) calculate an Fe2+/Fe3+ ratio using assumptions of perfect mineral stoichiometry and charge balance. Since almost all iron-bearing minerals contain both Fe2+ and Fe3+, the first two treatments are obviously unsatisfactory. |
| Databáze: | OpenAIRE |
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