Fe²⁺ and Fe³⁺ ordering in babingtonite Ca₂(Fe³⁺, Fe²⁺, Mn)₂Si₅O₁₄(OH) from the Yakuki mine, Fukushima, Japan: Valence-contrast analysis via single-crystal anomalous X-ray scattering (AXS) analysis

抄録

The distributions of Mn²⁺, Fe²⁺ and Fe³⁺ in babingtonite Ca_2.00Fe_0.64²⁺Fe_0.98³⁺Mn²⁺_0.27Mg_0.09Al_0.02Si₅O₁₄(OH) from the Yakuki mine, Fukushima, Japan are revealed via single-crystal anomalous X-ray scattering (AXS). The ordered distribution of Mn²⁺ at the Fe1 site is readily confirmed via Mn-AXS analysis based on the intensity difference observed in a pair of datasets measured at E_M1 = 6.388 keV and E_M2 = 6.513 keV below the Mn K absorption edge. The distributions of Fe²⁺ and Fe³⁺ are quantitatively determined for the first time using a dataset measured at E_F3 = 7.116 keV, where a significant difference in the anomalous scattering factor is observed between Fe²⁺ and Fe³⁺. This study quantitatively determines the site occupancies of Mn²⁺, Fe²⁺, and Fe³⁺ in babingtonite based on experimental evidence obtained from advanced AXS analysis. The present AXS analysis confirms the structural-chemical formula Ca_2.00(Fe_0.64²⁺Mn²⁺_0.27Mg²⁺_0.09)^Fe1(Fe_0.98³⁺Al³⁺_0.02)^Fe2Si₅O₁₄(OH) for babingtonite from the Yakuki mine.