Ideal associated solutions: application to the system albite-quartz- H₂O

The theory of associated solutions provides a simple but rigorous framework for the use of speciation reactions to model nonideal mixing behavior of silicate melt components. Application of the theory of the system Ab-Qz-H₂O requires only P-T solidus data in the anhydrous and H₂O-saturated systems Ab-H₂O and Ab-Qz-H₂O to calibrate equilibrium constants of proposed modeling reactions. Investigation of the systems Ab-H₂O and Ab-Qz-H₂O indicates that if a modeling reaction producing a sodium silicate species is considered, neither interaction between albite and silica melt to produce new complexes nor nonideal mixing of species is required and agreement between predicted and experimental eutectic compositions can be obtained by considering only disproportionation in albite melts. The thermodynamic consequence of these assumptions is that the Ab and Qz melt components mix ideally. -from Authors