The nucleation and further crystallization of vaterite on gallium (III)-oxide was investigated by the constant composition technique. The apparent order of the crystallization process was found to be 1.17+/-0.15 indicative of a surface diffusion controlled mechanism. The number of ions forming the critical nucleus was found to be n* = 3. We explore the mechanism of vaterite nucleation on gallia by the PM5 method included in the MOPAC program package. The surface energy of the growing phase was found to be 26.4+/-2.7 mjm(-2). (C) 2004 Elsevier B.V. All rights reserved.