Although usually the anion of the mineralizer is most active in dissolving the nutrient material, the cation also exerts an influence in some cases. The mineralizer can interact with impurities on the surface of the crystal and increase the growth rate. For example, the growth rate for sapphire (AlO) and zincite (ZnO) in potassium-containing solution (KOH, KCO) is higher in comparison to that in sodium-containing solution (NaOH, NaCO). This difference is not readily understood, but are attributed the interaction between potassium and an impurity absorbed on the surface.