Ti(3+) in meteoritic and synthetic hibonite

摘要: Electron spin resonance has been used to make the first direct determination of Ti^(3+) in synthetic hibonite and from inclusion SH-7 Murchison C2 chondrite. concentrations range 0.02 0.64 wt% blue 0.35–0.44 SH-7. No could be detected orange hibonite, supporting earlier conclusion that orange-to-blue transition is associated with presence Ti^(3+). At constant temperature oxygen fugacity, Ti^(3+)/Ti^(4+) increases decreasing V but not strongly dependent on bulk Ti. concentration levels encountered meteoritic Fe Cr contents do have a significant effect amount Ti^(3+). In both occupies 5-coordinated crystallographic site, which consistent formation doubly ionized vacancies. low fugacities, essentially all Ti^(4+) five-fold Al-site reduced Ti^(3+). Hibonite equilibrated gas as reducing solar composition. This other estimates based mineral equilibria high fugacities Ca-Al-rich inclusions. With possible exception Mo-W depletions, indicators trace element CAIs are inconclusive. There considerable evidence cooled lower temperatures, they experienced conditions significantly more oxidizing than those gas, perhaps planetary environments.