Oxidation state and coordination of Fe in minerals: An FeK-XANES spectroscopic study

High-resolution Fe K-edge XANES spectra of a series of crystalline Fe2+- and Fe3+-bearing model compounds were measured in an effort to correlate characteristics of the pre-edge feature with oxidation state and local coordination environment of Fe atoms. The model compounds comprise 30 natural minerals and synthetic compounds, with Fe coordination environments ranging from 4 to 12 O atoms for Fe2+, including 5-coordinated trigonal bipyramidal Fe2+, and from 4 to 6 O atoms for Fe3+. Most pre-edge spectra show two components (due to crystal-field splitting) that are located just above the Fermi level.