Calcium environment in omphacitic pyroxenes: XANES experimental data versus one-electron multiple scattering calculations
Paris, Eleonora; Wu, Ziyu; Mottana, Annibale; Marcelli, Augustο
European Journal of Mineralogy Volume 7 Number 5 (1995), p. 1065 - 1070
published: Oct 5, 1995
manuscript accepted: Apr 7, 1995
manuscript received: Aug 12, 1994
ArtNo. ESP147050705003, Price: 29.00 €
Abstract One-electron multiple scattering calculations are used to model the local environment of calcium in three pyroxenes (diopside, intermediate ordered omphacite, and jadeite-rich disordered omphacite) starting from their crystal structure data. The calculated Ca K-edge spectra agree well with the experimental X-ray absorption XANES spectra. The overall comparison of theory and experiment supports the model that Ca in omphacite is distributed over two non-equivalent sites, one having the same geometry as the Ca site in diopside, and a second one that of Na in jadeite. We stress the need of comparing the measured XANES spectra with ab-initio calculated spectra in order to gain a full understanding of experimentally observed features and deduce from them the crystal-chemical behaviour of individual cations present in a mineral structure.