This award is to determine experimental equilibrium solubilities of corundum, and andalusite plus quartz; geologically important minerals, at elevated temperatures (400 to 650 C) and pressures (up to 3 kbar) in acid solutions and aqueous salt fluids (0.05, 0.1, 0.5, 1.0 molal HCl and NaCl). The experiments supported by this award will involve extracting fluid samples while they are at high pressure and temperature with a unique hydrothermal apparatus and then determining the concentration of all volatile and non-volatile constituents of the fluid through a battery of modern analytical techniques. An important part of the theoretical analysis is that activity coefficients of neutral species must be considered when determining the equilibrium. Hopefully a model of Al speciation as a function of pH and ionic strength as well as pressure and temperature can be constructed in the Al2O-H2O-NaCl-HCl system. The proposed experiments should put limits on the possible solution compositions from which aluminum can be transported and aluminum bearing phases precipitate during metamorphism of the earth's crust.