Oxidation state and distribution of Fe in pumpellyite from Chichibu belt, Ozu, Ehime, Japan

Abstract

Oxidation state and distribution of Fe in pumpellyite was studied using Mössbauer and X-ray Rietveld methods. The sample was collected from greenstones, Chichibu belt, Ehime Prefecture. The pumpellyite contained 10.01wt.% total Fe₂O₃ on average. By applying the Fe²⁺:Fe³⁺-ratio determined by the Mössbauer analysis, and the Rietveld method together with chemical analysis, the resulting formula of Chichibu pumpellyite is (Ca_7.95Na_0.01K_0.02)_Σ7.98(Al_1.58Mg_1.21Fe³⁺_0.61Fe²⁺_0.53Mn_0.09)_Σ4.02(Al_6.51Fe³⁺_1.49V_0.02Ti_0.01)_Σ8.03Si_12.25O_40.75(OH)_15.25. The intracrystalline distribution coefficient of Fe³⁺ and Al between the X and Y sites [K_D = (Fe³⁺/Al)X/(Fe³⁺/Al)Y] is 1.69, indicating a stronger preference of Fe³⁺ in the X site.