Kinetics of cation distribution in cobalt-containing olivine, (Co0.6Mg0.4)2SiO4

Abstract

In olivines, (A,B)₂SiO₄, the A and B cations are distributed over two non-equivalent sites of octahedral coordination, M1 and M2. In the case of temperature dependent cation distributions, the kinetics of cation redistribution between these two sublattices can be studied by means of temperature-jump experiments. In situ experiments of this type are reported for a cobalt-containing olivine single crystal, (Co_0.6Mg_0.4)₂SiO₄. The relaxation experiments were performed by means of optical spectroscopy under in situ conditions in the temperature range between 480 and 690 °C yielding an activation energy of about 2.0 eV. The results are discussed in the framework of microscopic models of cation sublattice exchange. Implications for quench experiments are addressed.