Activation energy of Co–Mg intersite exchange in olivine, (Co0.6Mg0.4)2SiO4

In Co–Mg olivines, cations are distributed over two non-equivalent sites of octahedral coordination, M1 and M2. The kinetics of Co–Mg intersite exchange between M1 and M2 sites for (Co0.6Mg0.4)2SiO4 were studied from 500 to 680 °C by in situ optical spectroscopy using temperature-jump relaxation. The relaxation times were obtained from modeling relaxation curves with a single exponential behaviour. The apparent activation energy of about 193 ± 9 kJ/mol for cation exchange between M1 and M2 sites in (Co0.6Mg0.4)2SiO4 was determined from the Arrhenius plots of the inverse relaxation times.