Nucleation can be divided into homogeneous nucleation and heterogeneous nucleation. Crystallization consists of two major events, nucleation and crystal growth. There are three mechanisms with which supersaturation occurs&colon; precipitation, nucleation, and metastable. Solidification occurs in two steps&colon; "nucleation" and "crystal growth". They act in the nucleation or inhibition of hydroxyapatite formation. Homogeneous nucleation is much rarer than heterogeneous nucleation. This is seen for example in the nucleation of ice in supercooled small water droplets. The reversal occurs gradually through the nucleation and growth of ferroelectric domains with opposite polarization. Experiments show that "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than . Crystal formation requires two steps&colon; nucleation and growth. In the nucleation stage solid particles form within the liquid. Branched actin networks are created as a result of this nucleation of new filaments. It is typically difficult to experimentally study the nucleation of crystals. It is much more common than homogeneous nucleation. Seed-mediated methods consist of two different stages&colon; nucleation and growth.