This proposal outlined a joint Cornell-Brown Universities research project to determine the diffusion properties of minerals in rocks at high pressures (up to 100 kbar) and temperatures (up to 1200oC). The objectives are to assess the degree to which chemical and isotopic equilibrium are attained during mantle and lower crustal processes; and to extend the capabilities of diamond anvil cells to permit moderate duration experiments under controlled temperature and pressure. Models will be developed in order to predict diffusion kinetics in various minerals at high temperature and pressures. Other applications will to models of mantle mineralogy and chemistry; basalt genesis; mantle chemical transport; and very high grade metamorphism and melting in deep crustal regions.