Fe and Mg local environment in the synthetic enstatite-ferrosilite join; an experimental and theoretical XANES and XRD study

Synthetic orthopyroxenes on the join Mg (sub 2) Si (sub 2) O (sub 6) -Fe (sub 2) Si (sub 2) O (sub 6) have been studied to interpret the variation in the XANES spectra due to the Mg-Fe substitution in the crystal structure. The experimental Fe K-edge and Mg K-edge spectra show variation of the peak intensities as a function of the chemical composition along the En-Fs join. At the Fe K-edge, the intensity ratio between the two most intense peaks varies linearly with En mole %. Theoretical spectra have been calculated both at the Fe and Mg K-edge to interpret the data. The spectra, obtained by locating Fe (or Mg) in M1 and M2 sites and weighting these contributions according to occupancy data from Rietveld structure refinement, reproduce the experimental spectra well, allowing discrimination of the total contributions to the total spectrum due to Fe (Mg) located at each site.