The determination of site occupancies in two natural olivines by ALCHEMI method using only Si atoms as the reference atoms

Abstract

The site occupancies of major and minor elements in two olivines have been determined by ALCHEMI method using only Si atoms as the reference atoms and assuming the homogeneities in the chemical composition. Since Si atoms in many silicate minerals occupy only the tetrahedral sites, they can be used for the reference atoms. Therefore, the analytical technique derived in this study is useful for the determination of the site occupancies not only in olivine in which Mg atoms show ordered distribution but also in other silicate minerals which contain SiO₄ tetrahedra. The determined site occupancies for Mg and Fe show weak preferences in M2 and M1 sites, respectively, which are opposite to those reported previously by ALCHEMI method. However the tendency of the preferences of the major elements (Mg and Fe) in this study is in accordance with those obtained by X-ray diffraction method. The site occupancies for minor elements, Mn and Ni, shows strong preferences in M2 and M1 sites, respectively, which are consistent with previous results by ALCHEMI method.