Poster Sessions vacant is not represented in this formula. The results in this study revealed not only the existence of Fe 3+ in olivine but also of the short range order of laihunite structure.Keywords: olivine, 57Fe Mossbauer, oxidized scoria and lava
P10.05.38Acta Cryst. (2008). A64, C502The oxidation state and distribution of Fe in pumpellyite from Chichibu belt, Ozu, Ehime, Japan Crystal structure of chromian pumpellyite was analyzed using singlecrystal X-ray diffraction method in order to investigate behavior of chromium between two independent octahedral sites in pumpellyite,The chromian pumpellyite was collected from basic schists in the Osayama ultramafic body, Okayama Prefecture, Japan. It is reddish gray. The Cr distribution is heterogeneous, and Cr2O3 content is highest around chromite, reaching 13.3 wt%. The Cr2O3 content of the chromian pumpellyite available for the structural analysis was 1.78 wt%. The structure was refined by a least-squares method, where Ca, Mg and Si were fixed at the W, X and Z, respectively, and the occupancies of Cr and Al at the X and Y sites were refined. The R-index for the nonhydrogen atoms is 5.03% for 1243 unique reflections. The refined occupancies of AlX, CrX, AlY and CrY are 0.22, 0.08, 0.94 and 0.04, respectively. By applying this result and EPMA data, the formula is established as (K0.02Na0.07Ba0.01Ca8.00)Σ8.10(Mn ] are greater than those of Mg-Al-pumpellyite, because of Cr substitution for Al. It is consistent with mean Y-O distances of 1.932Å for the Osayama chromian pumpellyite and 1.918Å for Mg-Al-pumpellyite. The calculated bond balance sums are consistent with the refined occupancies of Al and Cr in the X and Y sites and the locations of OH at O5, O7, O10 and O11.