A Thermodynamic Model for Hydrous Silicate Melts

A simple thermodynamic model describing hydrous silicate melts has been applied to the systems albite-, diopside-, and silica-H₂O. The model is based on the assumption of ideal mixing of hydroxyl groups, H₂O molecules, and oxygens in the melt. Calculated and experimentally determined freezing-point depressions and H₂O solubilities for these systems are in agreement over substantial pressure and temperature intervals. The success of this model in accounting for observed phase equilibria of hydrous systems and its consistency with spectroscopic measurements of the concentrations of H-bearing species in glasses suggests that it accurately represents the interaction between H₂O and silicate melts at a molecular level.