ABSTRACT

Three series of solid solutions of orthopyroxene structure, (Fe, Mg )SiO₃, (Co, Mg)SiO₃ and (Ni, Mg)SiO₃, were synthesized, using high pressure sintering technique. Unit cell parameters of the synthesized pyroxenes were determined at room temperature. The deviation from Vegard's law is remarkable for both iron and nickel pyroxene series, whereas almost absent for cobalt one. It is suggested that the dominant factors which determine the distribution of ions among nonequivalent sublattice sites are 1) the difference in effective sizes of both ions (for the case of (Fe, Mg )SiO₃) and 2) the crystal field stabilization energy (for the case of (Ni, Mg )SiO₃). The nearly ideal behavior of (Co, Mg )SiO₃ is a result of the compensation between these two competing factors.