Pressure-induced structural changes in Eu-doped CaCO3 have been studied by time-resolved optical fluorescence spectroscopy and by total X-ray scattering combined with a pair distribution function analysis. Time-resolved fluorescence measurements are ideally suited to distinguish between calcitic and aragonitic local environments around the Eu-ions. We show that at ambient temperature calcite transforms at ∼10 GPa into an amorphous phase which locally has an aragonitic structure. This local structure is maintained on pressure release. The decay times of aragonite and the amorphous phase with a locally aragonitic structure are substantially longer than those of calcite.