Modeling of the temperature dependence of the excess properties of mixing of feldspars

Experimental data on phase equilibria were matched with calorimetric and cr ystallographic data on K-Ca-Na feldspars by thermodynamic modeling of a ter nary feldspar solid solution. The excess functions of mixing were described by original thermodynamic models based on the temperature-dependent terms of the excess heat capacity. The proposed models were compared with the mod el based on the generally accepted Margules entropy and enthalpy series, wh ich gives a linear approximation of the temperature dependence of the free energy of mixing. It was shown that the proposed thermodynamic models are n ot worse than the linear approximation of the free energy of mixing and hav e some positive features.