Crystallization is the (natural or artificial) process of formation of solid crystals precipitating from a solution, melt or more rarely depositeddirectly from a gas. Crystallization is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs. In chemical engineering crystallization occurs in a crystallizer. Crystallization is therefore an aspect ofprecipitation, obtained through a variation of the solubility conditions of the solute in the solvent, as compared to precipitation due to chemical reaction.
PROCESS:
The crystallization process consists of two major events, nucleation and crystal growth. Nucleation is the step where the solute molecules dispersed in the solvent start to gather into clusters, on the nanometer scale. The crystal growth is the subsequent growth of the nuclei that succeed in achieving the critical cluster size. Nucleation and growth continue to occur simultaneously while the supersaturation exists.
Crystallization in nature
There are many examples of natural process that involve crystallization.
Geological time scale process examples include:
 Natural (mineral) crystal formation (see also gemstone);
 Stalactite/stalagmite, rings formation.
Usual time scale process examples include:
 Snow flakes formation (see also Koch snowflake);
 Honey crystallization (nearly all types of honey crystallize).
Artificial methods
For crystallization (see also recrystallization) to occur from a solution it must be supersaturated. This means that the solution has to contain more solute entities (molecules or ions) dissolved than it would contain under the equilibrium (saturated solution). This can be achieved by various methods, with (1) solution cooling, (2) addition of a second solvent to reduce the solubility of the solute (technique known as