The crystal structures and the cation distributions of Mg and Fe of natural olivines

Abstract

The crystal structures of seventeen natural Mg–Fe olivines from nine rock specimens of seven different rock types were refined by X-ray diffraction method. Intensity data of the two olivines were also obtained at high temperatures ranging from 200°C to 700°C. The site occupancy refinements of the unheated olivines showed that volcanic olivines and a metamorphic olivine have a slight preference of Fe for the M1 and M2 sites, respectively. In-situ high temperature X-ray experiments showed that the K_D (= Fe/Mg)_M1/(Fe/Mg)_M2 values of the heated olivines increased with increasing temperature, and the K_D values of the olivines heated above 600°C increase with increasing fayalite content.