One of the most debated effects the magnetic fields exert on aqueous solutions and dispersions is their influence on the crystal structure of the main scale component, CaCO3. This study presents the results of an experimental program performed to quantitatively evaluate influence of the key magnetic treatment parameters-magnetic induction, exposure time, and fluid velocity-on the polymorph composition of CaCO3, precipitated from carbonized aqueous solutions. The results show that magnetic treatment favored the precipitation of aragonite. The key treatment parameters affecting the aragonite content were the magnetic induction and the exposure time, while the fluid velocity exerted no significant influence. The magnetic field has no significant influence oil the zeta potential of the precipitated particles in any stage of the treatment. These experimental findings indicate that the magnetic field influence on the crystal structure of CaCO3 cannot be attributed to the magnetohydrodynamic influence on the charge distribution within the electrical double layer of the forming crystallites. The results rather suggest that the magnetic fields influence the CaCO3 polymorph phase equilibrium either by influencing the CO2/water interface or through the hydration of CO32- ions prior to the formation of stable crystal nuclei in the solution. (C) 2004 Elsevier Inc. All rights reserved.