オホーツク石におけるFe^<3＋>およびMn^<3＋>の席選択性

Distribution of Mn^<3＋> and Fe^<3＋> in the X and Y-sites of okhotskite，an (Mn^<3＋>)-dominant pumpellyite group mineral，has been investigated．The okhotskite sample was separated from the manganiferous iron ore in the Tokoro belt，Hokkaido，Japan．Very small amounts of hematite and piemontite remained as impurity．The average values of 32 point analyses are 33.55 SiO_2，0.15 TiO_2，7.85 Al_2O_3，0.10 V_2O_3，5.08 total Fe_2O_3，25.44 total Mn_2O_3，0.02 NiO，1.68 MgO，20.68 CaO，0.15 SrO and 0.04 Na_2O．Total Fe_2O_3 and total Mn_2O_3 range 1.14-6.95 and 22.52-29.56 wt．%，respectively．H_2O content given by TG analysis is 6.25 wt．%，which corresponds to the weight loss at 717 and 829℃．(^<57>)Fe M&ouml;ssbauer spectrum of the sample consists of two doublets by Fe^<3＋> in the X and Y-sites of okhotskite and very weak peaks by hematite．The doublet of IS=0.363 mm/s and QS=1.16 mm/s is attributed to Fe^<3＋> in the X-site and that of IS=0.43 mm/s and QS=2.18 mm/s to Fe^<3＋> in the Y-site．Area ratio of the doublets shows that 95 atomic % of total Fe^<3＋> distributes in the X-site and remaining Fe^<3＋> is in the Y-site．By using the average composition，H_2O content and results by M&ouml;ssbauer analyses of okhotskite，the (Mn^<3+>_Y)／(Mn^<3＋>_X) ratio is derived to be 19.5．Thus the site preferency of Al，Mn^<3＋> and Fe^<3＋> in the Y-site is (Al)＞(Mn^<3＋>)＞(Fe^<3＋>)．On calculating structural formula of pumpellyite-okhotskite series minerals，the Y-site should be filled by Al，Mn^<3＋> and Fe^<3＋> in this order．