Octahedral cation partitioning in Mg,Fe2+-olivine.: Mossbauer spectroscopic study of synthetic (Mg0.5 Fe2+0.5)2SiO4 (Fa50)

The high-temperature partitioning of Fe2+ and Mg between the two non-equivalent octahedral M1 and M2 sites in synthetic olivine (Fa(50)) was studied by Mossbauer spectroscopy. Powder samples have been equilibrated in annealing experiments performed under reducing oxygen fugacity at temperatures between 500 and 800 degrees C followed by rapid quenching in order to prevent redistribution of cations. M-site ordering with Fe2+ preferring M1, Mg preferring M2 sites increases continuously with rising equilibrium temperature. K-D values increase from 1.21 at 500 degrees C to 1.48 at 750 degrees C. The results are consistent with both room temperature as well as in situ high temperature single crystal X-ray diffraction experiments of Heinemann et al. [8, 9].