1. Introduction: Thermodynamic Data Systematics.- 2. Thermodynamic Relations.- Temperature and pressure dependence of the Gibbs free energy.- Heat capacity at high temperature.- Estimation of Cv.- Method of optimization.- Anderson's enthalpy/bulk modulus relationship.- Some comparisons.- Molar volume at high pressure and high temperature.- The use of the Birch-Murnaghan (BM) equation at high temperature.- Comparison with Anderson's model.- 3. Techniques for Data Assessment.- Computational techniques.- The manual adjustment approach using free energy minimization.- The regression technique.- The optimization technique.- Phase equilibrium calculation by SOLGASMIX.- 4. Assessment of Data on Some Oxides and Silicates: Calorimetry and Low-pressure Phase Equilibrium Experiments.- The system Si02.- Andalusite, kyanite and sillimanite.- Wollastonite, gehlenite, akermanite and monticellite.- Enstatite and pyrope.- Forsterite.- Fayalite and ferrosilite.- Orthodiopside.- Clinoenstatite.- Diopside.- Hedenbergite.- Ca-tschermak, anorthite and grossular.- Almandine and hercynite.- Spessartine.- Rutile and ilmenite.- Sanidine and muscovite.- Jadeite, albite and paragonite.- Phlogopite.- Annite and phlogopite-annite solution.- Talc and anthophyllite.- Brucite, chrysotile and antigorite.- Grunerite.- Ferrocordierite and the cordierite-ferrocordierite solution.- Hydrous cordierite.- 5. Assessment of Data on Some Oxides and Silicates: Calorimetry and High-Pressure Phase Equilibrium Experiments.- System Fe-0.- Polymorphism of Fe.- Wustite.- Magnetite and hematite.- System MgO-SiO2.- Polymorphism of SiO2.- Polymorphism of Mg2Si04.- Polymorphism of MgSi03.- System FeO-SiO2.- Polymorphism of Fe2SiO4.- Polymorphism of FeSiO3,.- 6. Assessment of Solid Solution Parameters for Some Silicates.- Solid solution models.- Gehlenite-akermanite.- Spinel-hercynite.- Forsterite-fayalite.- Forsterite-monticellite.- Fayalite-monticellite.- Enstatite-ferrosilite.- Enstatite-diopside.- Clinoenstatite-jadeite.- Diopside-jadeite and hedenbergite-jadeite.- Muscovite-paragonite.- Phlogopite-annite.- Cordierite-ferrocordierite.- Cordierite-hydrous cordierite and ferrocordierite-hydrous cordierite.- Anorthite-albite, anorthite-sanidine and albite-sanidine.- Interaction parameters.- References.- Appendix I: Tables of Thermodynamic Data.- Appendix II: Summary of Reactions in the Mg-Fe-Si-O system.- Species Index.