Computation of Multicomponent Phase Equilibria

Abstract

With the publication of thermodynamic data by Helgeson et al. (1978) and Robie et al. (1978), we have data on the Gibbs free energy of formation of many geologically important substances. It is, therefore, appropriate to consider suitable techniques of calculating multicomponent phase equilibria. Geochemists and petrologists are familiar with the method of equilibrium constants used in the calculation of equilibrium pressure and temperature for single or multiple reactions. This is the method which, for example, has been used by Helgeson et al. in deriving the free-energy data on many minerals. Once there is an accumulation of a sizable amount of such data, the method of minimization of total Gibbs free energy as described here may be used advantageously to calculate equilibrium assemblages. With this method, it is not necessary to write down any specific reactions and little chemical intuition or experience is needed to predict the course of complex equilibria. This method, although used by some geochemists (e.g., Grossman, 1972) in nebular condensation calculations, has not been given due attention by petrologists (but see Brown and Skinner (1974) and Nicholls (1977) for alternative methods).