In Part I (Vinograd, 2002) the relationship between temperature, composition and free energy of the diopside–jadeite solid solution was described using a CVM model. Here the same relationship is described using a combination of Redlich-Kister (RK) polynomials and Gaussian functions. The use of the Gaussians permits an accurate description of the free energy dip centred at Jd50, which is caused by the long-range ordering, while the effect of the short-range ordering can be easily modelled using the RK polynomial The simplified RK-Gaussian description is extended to the three-component diopside–jadeite–hedenbergite solid solution. The polynomial description permits an easy incorporation of the derived activity-composition relations into phase-equilibrium computation software.

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