Synthetic Mg-Fe-Ni olivines annealed at 1000 degrees C have been studied. The site populations of Fe (super 2+) , Mg (super 2+) and Ni (super 2+) among the M1 and M2 sites have been determined by a combination of Moessbauer spectroscopy and the profile-fitting technique based on X-ray powder diffraction data. The Mg (super 2+) -Fe (super 2+) cation distribution coefficient, K (sub D = [X Fe (Ml). X Mg (M2)]/[X Fe (M2) . X Mg (Ml)], is close to unity but slightly decreases with increasing nickel content. The Ni (super 2+) -(Mg (super 2+) +Fe (super 2+) ) cation distribution is close to that of Ni (super 2+) -Mg (super 2+) earlier reported for some synthetic Ni-Mg olivines.--Journal abstract.

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