The pressure stability of kyanite was experimentally reversed with the use of a multi-anvil apparatus. Kyanite was found to decompose into its oxides stishovite and corundum between 14+ or -0.5 GPa (at 1000 degrees C) and 17.5+ or -1.0 GPa (at 2000 degrees C). Reliable thermodynamic calculations can be performed to temperatures of approximately 1500 degrees C. Up to this temperature, the location of the equilibrium kyanite = corundum + stishovite, determined in this study, constrains the equilibrium coesite = stishovite. A set of thermodynamic data was calculated by linear programming from the kyanite breakdown reaction and the coesite = stishovite equilibrium. Feasible values for the fitted thermo-dynamic properties are -28.5 to -26.3 MPa/K for the temperature derivative of the bulk modulus [(dK/dT) p ] of kyanite, -815254 to -813635 J/mol for G 0 (sub (1298)) of stishovite, and 24.6 to 26.3 J/mol.K for S 0 (sub (1298)) of stishovite. The experimental results indicate (1) that in peraluminous eclogites of basaltic or sedimentary origin, stishovite may coexist stably with corundum at a depth greater than 420-450 km and (2) that in an inhomogeneous Al-enriched mantle, corundum could be a minor constituent in the lower mantle.