Prenucleation Clusters and Non-classical Nucleation

In this contribution, we review the recent literature on an alternative crystallization pathway involving stable clusters prior to nucleation and show that the prenucleation cluster pathway is a truly non-classical concept of nucleation. Prenucleation clusters are solutes with "molecular" character in aqueous solution. It becomes evident that the stable clusters may have been concealed by the so-called ion pair concept and activity effects. We show that non-classical nucleation via stable prenucleation clusters is a highly valuable concept for a novel understanding of phenomena observed in bioand biomimetic mineralization, which however may hardly be rationalized by means of classical nucleation theory. The importance to combine experimental and theoretical studies is emphasized.