Simultaneous consideration of Moessbauer and/or experimental phase equilibrium data for epidote, andradite, and hedenbergite together with the thermodynamic properties of aqueous species, CO/sub 2/-H/sub 2/O fluids, and coexisting minerals permits comprehensive analysis of mineral stabilities and the effects of preferential site occupancy and solid solubility on hydrothermal solution compositions in the system CaO-FeO-Fe/sub 2/O/sub 3/-Al/sub 2/O/sub 3/-SiO/sub 2/-H/sub 2/O-CO/sub 2/ at high pressures and temperatures. Assuming substitutional order/disorder in epidote solid solutions to be independent of composition together with random mixing and equal interaction of cations on energetically equivalent sites in garnet and epidote solid solutions permits calculation of the extent of Al/sup 3 +/ and Fe/sup 3 +/ partitioning between coexisting garnet and epidote. The results of these calculations agree closely with published compositions of garnet and epidote solid solutions in skarn deposits, low-grade metamorphic rocks, and geothermal systems.
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Bird et al. (1980) studied this question.