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The high-temperature partitioning of Fe 2+ and Mg between the two nonequivalent octahedral M1 and M2 sites in synthetic olivine (Fa 50 ) was studied by Mö ssbauer spectroscopy. Powder samples have been equilibrated in annealing experiments performed under reducing oxygen fugacity at temperatures between 500 and 800-C followed by rapid quenching in order to prevent redistribution of cations. M-site ordering with Fe 2+ preferring M1, Mg preferring M2 sites increases continuously with rising equilibrium temperature. K D values increase from 1.21 at 500-C to 1.48 at 750-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].

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