A thermodynamic treatment of chemical reactions in orthopyroxene

Abstract

Mixing of Fe and Mg in orthopyroxene crystalline solution can be represented by a multicomponent regular solution model when the molecules (Mg^M1Mg^M2Si₂O₆, Fe^M1Fe^M2Si₂O₆, Fe^M1Mg^M2Si₂O₆ and Mg^M1Fe^M2Si₂O₆) are introduced as its components. In this regular solution model, there are three independent interaction parameters (W^M1, W^M2 and W^M12) which correspond to the cation interactions between M1 and M1 sites, M2 and M2 sites and M1 and M2 sites, respectively. These parameters can not be determined uniquely by site-occupancy measurements only. Some thermodynamic formulations for orthopyroxene are given by using these parameters.