The solubility of natural grossular-rich garnet in pure water at high pressures and temperatures

The Solubility of a natural grossular-rich garnet of composition Ca(2.86)Fe(2+) (0.07)Mg(0.07)Fe(3+) (0.10)Al(1.90)Si(3.00)O(12) has been experimentally determined in pure water at pressures from 1 to 5 GPa and temperatures ranging from 400 to 800 degrees C with the weightloss 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-Al(2)O(3)-SiO(2) system, the solubility of grossular is considerably lower than that of quartz (SiO(2)) or wollastonite (CaSiO(3)), but higher than that of corundum (Al(2)O(3)) 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, rho(H2O), we suggest that the following expression provides an acceptable description of the solubility of pure grossular, Ca(3)Al(2)Si(3)O(12), in water for the above pressure-temperature range: log (m(grs)) = 0.8639 - 3519.71*T(-1) + 676921.07*T(-2) + 4502.85*T(-3) + log rho(H2O)*(7.2557 + 773.65*T(-1) - 106080.98*T(-2)), where m(grs) is the molality of dissolved grossular and T is in degrees C. Uncertainties estimated from the outer bounds of experimental data scatter indicate a maximum of +/- 0.045 mol(grs)/kg H(2)O. Comparison with available experimental solubility data on quartz, wollastonite, corundum and kyanite provides indirect evidence for the presence of aqueous Al-Si-species.