Phase boundaries for the reactions CaGeO3 (wollastonite→garnet) and CaGeO3 (garnet→perovskite) were determined at high pressure and temperature. The enthalpies of these transitions were measured by high temperature calorimetry. These studies indicate a positive dP/dT for the wollastonite-garnet transition and a negative dp/dT for the garnet-perovskite transition. These PT slopes are further supported by calculations of lattice vibrational entropies based on Kieffer's model and the infrared and Raman spectra of the three polymorphs.