Rates of kyanite->andalusite and kyanite->sillimanite conversions: Effect of water pressure

The rates of kyanite --> andalusite and kyanite --> sillimanite conversions were studied at T = 820 degrees C and pressures of 0.5-5 bar. The pressure limits within which the conversion rates vary nearly linearly in relation to the thermodynamic affinity (the quantity proportional to the pressure departure from the equilibrium value) are established at ca. 7.4-3.5 and 9.9-1.5 kbar, respectively. At lower pressures, the conversion rates decrease dramatically. The kyanite --> andalusite conversion decreases linearly as the partial water pressure decreases. The data presented substantiate the previously deduced kinetic equations of polymorphous transformations in Al2SiO5.