Acid-base properties and structons: towards a structural model for predicting the thermodynamic properties of silicate melts

Phase equilibrium relationships in igneous systems can be estimated using empirical mathematical models based on
multi-component regular solution formulae. Although these provide useable results within the fitted region, they can
give very misleading values outside the compositional range of curve fitting. Moreover, they usually give poor estimates
of the well-characterized melting relations of simple systems and do not relate to the large body of thermodynamic
activity data available in the metallurgical literature, nor to spectroscopic, diffraction or computational models
of silicate melt properties. The aim of this paper is to extend previous acid-base models of silicate melts and to
use a quasi-chemical model to calculate the activities of quasi-chemical silicate mixing units, or structons, from combinations
of the oxo-species used in quasi-chemical and polymer models to calculate oxide activities in metallurgy.