Abstract
X-ray Absorption Near-Edge Structure (XANES) analysis of the calcium K-edge of a series of natural pyroxenes is reported. The samples belong to the solid solution series diopside (CaMgSi2O6) — jadeite (NaAlSi2O6). In diopside, the M2 site is occupied by Ca only, but along the join Na substitutes Ca in this position. From XANES analysis of different samples we found a distortion of the polyhedron around the M2 site varying as a function of Ca content. This is probably due to compression of the site in a selected direction with an unchanged average distance, so that the coordination around the Ca atom changes from the 4-2-2 configuration typical of the diopside structure to the 6-2 configuration typical of Na in the jadeite structure. Intermediate pyroxenes exhibit both configurations, and acquire therefrom the structural order as already detected by X-ray diffraction techniques.
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Davoli, I., Paris, E., Mottana, A. et al. Xanes analysis on pyroxenes with different ca concentration in M2 site. Phys Chem Minerals 14, 21–25 (1987). https://doi.org/10.1007/BF00311144
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DOI: https://doi.org/10.1007/BF00311144