Thermodynamics of formation of the silicates and germanates of some divalent transition metals and of magnesium

The enthalpies of formation of Mg₂SiO₄, Co₂SiO₄, Ni₂SiO₄, Zn₂SiO₄, Mg₂GeO₄, MgGeO₃, Co₂GeO₄, CoGeO₃, Ni₂GeO₄, and Zn₂GeO₄ from the component oxides were measured by solution calorimetry in a molten oxide solvent at 692±2°C. Regularities in the thermodynamics of formation of the silicates and germanates of Mg, Mn, Fe, Co, Ni, Cu, and Zn are discussed, entropies of formation calculated when possible, and some thermodynamic manifestations of the possible polymorphism (olivine, spinel, phenasite) in these systems are noted.