The formation of calcium carbonate is a common ionic reaction that takes place in natural processes and in various technologies. In spite of the simplicity of the reaction, there is a considerable variability in the properties of the solid product, such as the crystal form, particle size distribution and the electrokinetic (zeta) potential. The influence of the magnetic field on calcium carbonate precipitation has been known for a long time and although many efforts have been made to explain this effect, researchers still disagree on the mechanism(s) responsible. The focus of this investigation was the influence of the magnetic field on the zeta potential of calcium carbonate precipitated from low-concentration water solutions of calcium hydrogencarbonate. The experiments were executed in parallel, with and without the presence of the magnetic field. The reaction is relatively slow and it is easy to follow the properties during precipitation. The observed system is pure and the influence of added impurities (ions of heavy metals) and other variables can be followed separately. In addition to the zeta potential, the particle size distribution of the precipitated calcium carbonate and its crystal form were determined.