Solution properties of almandine-pyrope garnet as determined by phase equilibrium experiments

The thermodynamic mixing properties of almandine-pyrope garnet were derived from phase equilibrium experiments at temperatures of 900 and 1000 °C and pressures from 8 to 14 kbar for the assemblage garnet + rutile + sillimanite + ilmenite + quartz (GRAIL). Almandine (Alm) has essentially ideal behavior in almandine-pyrope garnet over the composition range Alm₈₉–Alm₆₁ at the above experimental conditions. In all experimental products a systematic partitioning of Fe and Mg between garnet and ilmenite was seen with ln K_d ≈ 1.59. This partitioning does not appear to be temperature sensitive. The results of this study support the use of garnet mixing models that incorporate ideal or nearly ideal Fe-Mg parameters.