Different forms of nucleation exist. The main difference between primary and secondary
nucleation is the presence of any crystal from the chemical that is crystallizing. Two types of
primary nucleation exist; homogeneous and heterogeneous. Homogeneous nucleation is the
formation of the solid phase when no solid phase exists. At heterogeneous nucleation, only
foreign solid phases exist. Secondary nucleation is a mechanism by which formation of the
solid phase is initiated by the presence of the solid phase of the crystallizing material itself