Electron probe microanalysis of Fe2+/ΣFe ratios in calcic and sodic-calcic amphibole and biotite using the flank method

We present an analytical approach to determine the Fe2+/ΣFe ratio in amphiboles and biotites using electron probe microanalysis (EPMA). The “flank method” applied in this study is based on the fact that FeL line spectra show different peak position and intensity for Fe2+ and Fe3+, which is associated with a resonant process involving both X-ray absorption and emission. The flank positions for Lα and Lβ, which correspond to sites with minimal...