The synthesis of calcium carbonate (CaCO3) crystals from aqueous solutions containing sodium dodecyl sulfate (SDS), poly(N-vinyl-l-pyrrolidone) (PVP), or SDS/PVP complexes has been performed through a slow titration method. It was found that aragonite and calcite co-existed in the prepared crystals. The formation of aragonite in the precipitation systems without magnesium ions indicates that at ambient temperature ca. 26.0degreesC, initially formed amorphous CaCO3 could also transfer into aragonite in the sedimentary phase, which indicates the controlling factor of organic additives in the nucleation and growth process of CaCO3 crystals. The appearance of hexagonal crystals in the suspensible phase confirmed the hexagonal crystallization cell of vaterite, and revealed the colloidal-dispersion function of the SDS/PVP complex in the crystallization process of CaCO3. (C) 2003 Elsevier B.V. All rights reserved.