Divalent chromium in ferropericlase inclusions in lower-mantle diamonds revealed by micro-XANES measurements

Abstract

Chromium K-edge X-ray absorption near-edge structure (XANES) spectra of natural ferropericlase were measured using an X-ray microbeam from a synchrotron radiation source to estimate the valence state of Cr. Measured samples were inclusions collected from lower-mantle diamonds. The obtained results revealed that divalent chromium is present in the materials in the lower mantle and that the proportion of Cr²⁺ in the total Cr content varied among the samples. The valence state of chromium in the inclusions in diamonds is a potential indicator of the redox conditions in the lower mantle.