A THERMODYNAMIC ANALYSIS OF THE SYSTEM LIALSIO4-NAALSIO4-AL2O3-SIO2-H2O BASED ON NEW HEAT-CAPACITY, THERMAL-EXPANSION, AND COMPRESSIBILITY DATA FOR SELECTED PHASES

Heat capacity, thermal expansion, and compressibility data have been o btained for a number of selected phases of the system NaAlSiO4-LiAlSiO 4-Al2O3-SiO2-H2O. All C-p measurements have been executed by DSC in th e temperature range 133-823 K. The data for T greater than or equal to 223 K have been fitted to the function C-p(T) = a + cT(-2) + dT(-0.5) + JT(-3), the fit parameters being [GRAPHICS] The thermal expansion d ata (up to 525 degrees C) have been fitted to the function V-0(T) = V- 0(T) [1 + nu(1) (T-T-0) + nu(2) (T-T-0)(2)], With T-0 = 298.15K. The r oom-temperature compressibility data (up to 6 GPa) have been smoothed by the Murnaghan equation of state. The resulting parameters are [GRAP HICS] These data, along with other phase property and reaction reversa l data from the literature, have been simultaneously processed by the Bayes method to derive an internally consistent thermodynamic dataset (see Tables 6 and 7) for the NaAlSiO4-LiAlSiO4-Al2O3-SiO2-H2O quinary. Phase diagrams generated from this dataset are compatible with cookei te-, ephesite-, and paragonite-bearing assemblages observed in metabau xites and common metasediments. Phase diagrams obtained from the same database are also in agreement [GRAPHICS] with the cookeite-free, peta lite-, spodumene-, eucryptite-, and bikitaite-bearing assemblages know n to develop in the subsolidus phase of recrystallization of lithium-b earing pegmatites. It is gratifying to note that the cookeite phase re lations predicted earlier by Vidal and Goffe (1991) in the context of the system [GRAPHICS] Li2O-Al2O3-SiO2-H2O agree with our results in a general way.