An internally consistent data set on the thermodynamic properties of the silica polymorphs stable up to 15 GPa (α-quartz, β-quartz, tridymite, cristobalite, coesite, and stishovite) and the liquid phase is presented. The data set was produced through a computer-based assessment of the properties in which the available thermochemical (calorimetric), physical (bulk modulus and thermal expansion), and solid-state and melting transition data (including some newly determined data on the high-pressure polymorphs coesite and stishovite) were considered. The data set can be used to calculate phase relations at pressures of 0.1 MPa to 15 GPa and temperatures of 30 to 3200 K. The calculated phase diagram using these data agrees quite well with the equilibrium determinations except for the high-temperature part of the coesite-stishovite boundary. The properties of the liquid phase obtained are also in good agreement with the available data. ¿ American Geophysical Union 1994