Ion exchange experiments between Fe-Mn-Mg olivine solid solution and 2N aqueous chloride solution were carried out at 600°C and 1 kbar. Continuous solid solution was formed under the experimental conditions. The cations are preferentially incorporated into the olivine solid solution in the order of Mg²⁺»Fe²⁺>Mn²⁺.
     In order to obtaine the mixing properties of the olivine solid solution, the experimental results were analyzed thermodynamically taking into consideration the aqueous speciation in the coexisting 2N aqueous chloride solution. As a result, a slightly negative excess Gibbs energy of mixing was obtained for a fayalite—tephroite solid solution, and positive ones for tephroite—forsterite and forsterite—faralite solid solutions.