ABSTRACT

The energy minimization program WMIN of BUSING (1970) has been applied to predict the crystal structures of mantle minerals at high pressure. The repulsive parameters, ionic radius A_i and softness parameter B_i (ionic compressibility) to be used in the predictions are evaluated for Mg²⁺, Si⁴⁺, Al³⁺, Ca²⁺, Fe²⁺ and O^2- ions by employing the cell dimensions and atomic coordinates of α-Mg₂SiO₄(olivine), Fe₂SiO₄ (fayalite), MgAl₂O₄(spinel) and CaMgSi₂O₆(diopside) determined at one atm. These parameters were then used to predict the u-parameter of γ-Mg₂SiO₄(spinel) by the energy minimization method of WMIN. The u-parameter, 0.3685 was obtained for the observed cell parameter a(=8.0649A). The method and the parameters will be applied to predict other stable minerals in Earth's mantle.