Ferric iron in Al-bearing akimotoite coexisting with iron-nickel metal in a shock-melt vein in an L-6 chondrite
We report evidence for high ferric iron to total iron (Fe3+/ΣFe) ratios in Al-bearing akimotoite coexisting with other high-pressure silicates and Fe-Ni metal from shock melt-veins in the Sixiangkou (L-6) chondrite. The measurements were made using electron energy-loss near-edge structure (ELNES) sp...
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Published in | The American mineralogist Vol. 92; no. 10; pp. 1545 - 1549 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Washington
Mineralogical Society of America
01.10.2007
De Gruyter Walter de Gruyter GmbH |
Subjects | |
Online Access | Get full text |
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Summary: | We report evidence for high ferric iron to total iron (Fe3+/ΣFe) ratios in Al-bearing akimotoite coexisting with other high-pressure silicates and Fe-Ni metal from shock melt-veins in the Sixiangkou (L-6) chondrite. The measurements were made using electron energy-loss near-edge structure (ELNES) spectroscopy. The results demonstrate that akimotoite in shock-melt veins of this meteorite has high proportions of Fe3+, with a Fe3+/ΣFe ratio of 0.67(3). In contrast, the coexisting majoritic garnet and ringwoodite, which are the typical Fe-bearing phases in shock veins in this meteorite, are enriched in Fe2+ rather than Fe3+, with Fe3+/ΣFe ratios of 0.10(5) and 0.15(5), respectively. We conclude that the higher affinity of Fe3+ for akimotoite, rather than for the other dense silicate phases, is related strongly to the substitution mechanism of trivalent cations. This mechanism is described as VI(A)Fe3+ + VI(B)Al3+ = VI(A)Mg2+ + VI(B)Si4+ in the ABO3 structural formula of MgSiO3-ilmenite under high pressures and temperatures, and operates even at a low oxygen fugacity where Fe-Ni metal is stable. |
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ISSN: | 0003-004X 1945-3027 |
DOI: | 10.2138/am.2007.2546 |