• journal_title：American Mineralogist
• Contributor：Nobuyoshi Miyajima ; Ahmed El Goresy ; Catherine Dupas-Bruzek ; Friedrich Seifert ; David C. Rubie ; Ming Chen ; Xiande Xie
• Publisher：Mineralogical Society of America
• Date：2007-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2007.2546
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：92
• issue：10
• firstpage：1545
• section：Articles

We report evidence for high ferric iron to total iron (Fe³⁺/∑Fe) 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⁺/∑Fe 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⁺/∑Fe 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.