The kinetics of vaterite (CaCO3) crystallization on calcite in the presence of glutamic acid was investigated by the constant composition method. The presence of glutamic acid in the supersaturated solution stabilizes this calcium carbonate polymorph. The number of ions forming the critical nucleus was found to be four and a surface energy of 12 mJ m(-2) was estimated. The apparent growth order was found to be 1.2 +/-0.2 typical for a surface diffusion-controlled spiral growth process.