This is a Presidential Young Investigator (PYI) award. The research project involves experimental studies of the kinetics and mechanisms of hydrothermal water-rock reactions. Specific objectives include investigations of: (1) rates and mechanisms of dissolution of minerals in aqueous solutions, (2) rates and mechanisms of diffusional healing of cracks in minerals and the influences of temperature, pressure, fluid flow, and fluid chemistry on the processes, (3) rates and mechanisms of water- enhanced deformation of minerals, and (4) kinetics of hydration and dehydration reactions. The research will also involve studies of the thermodynamics and chemistry of natural brines from a variety of geologic settings. The results of these studies will enhance our understanding of the important role of aqueous fluids in geochemical dynamics.