The solubility of a natural grossular-rich garnet of composition Ca2.86Fe2+0.07Mg0.07Fe3+0.10Al1.90Si3.00O12 has been experimentally determined in pure water at pressures from 1 to 5 GPa and temperatures ranging from 400 to 800 °C with the weight-loss technique in piston–cylinder apparatus. Grossular dissolves congruently in this pressure–temperature region. The amount of dissolved grossular increases with both increasing pressure and temperature and ranges from 0.1 to 7.0 wt.%. In comparison to available data on other phases in the CaO–Al2O3–SiO2 system, the solubility of grossular is considerably lower than that of quartz (SiO2) or wollastonite (CaSiO3), but higher than that of corundum (Al2O3) at comparable pressure–temperature conditions. Using a model based on the familiar correlation between the equilibrium constant of a dissolution reaction and the density of water, ρ H2O, we suggest that the following expression provides an acceptable description of the solubility of pure grossular, Ca3Al2Si3O12, in water for the above pressure–temperature range:
where mgrs is the molality of dissolved grossular and T is in °C. Uncertainties estimated from the outer bounds of experimental data scatter indicate a maximum of ±0.045 molgrs/kg H2O. Comparison with available experimental solubility data on quartz, wollastonite, corundum and kyanite provides indirect evidence for the presence of aqueous Al–Si-species.