Solvi of the nepheline-kalsilite mineralogical system have been investigated by conducting both chemical homogenization and unmixing experiments for two nepheline-kalsilite series that differ in excess silicon. Reversed phase equilibria demonstrate that relatively small differences in Si content produce a 130 degrees to 150 degrees C difference in the critical temperature of the solvus. The higher critical temperature of the more siliceous series correlates well with greater Gibbs free energies and enthalpies of K-Na mixing. The nepheline-system ([ ]Si = (K,Na)Al) on the thermodynamic mixing properties of another (K = Na) and in turn the significant influence of Si on phase behavior.
Title
The effects of excess silicon on immiscibility in the nepheline-kalsilite system
Hovis, G. L. and J. A. Crelling. (2000 Mar.) "The effects of excess silicon on immiscibility in the nepheline-kalsilite system." American Journal of Science 300 (3): 238-249 .