The influence of pH on the growth inhibitory effect of additive Ca 2+ ions on CaCO Influence of pH in the Presence of Additive Ca 2+ ions Crystal Form Previous studies report that calcite only predominates in high pH conditions, regardless of the presence or concentration of impurity or additive ions. However, the X-ray diffractograms presented in Figure show that pH variations has no effect on the polymorph of the synthesized particles, when additive Ca 2+ ions are present in the suspension. Regardless of the pH, pure calcite phases crystallized even in low alkaline pH conditions known to favor the crystallization of vaterite. It indicates that, besides a high pH, additive Ca 2+ ions also influence the polymorph selectivity. Similarly, Mg 2+ ion has been reported