define the process used for obtaining solid crystals of a substance from its saturated solution
Crystallisation is the process of slow precipitation of solid crystals of a substance from a concentrated homogeneous solution. It is basically a separation method in which a substance is transferred from the liquid (i.e. solution) phase to the solid state. The substance is thus obtained in pure crystalline form and has no impurity. It is used by chemists for the purification of solid substances.
Crystallization is the (natural or artificial) process where a solid forms where the atoms or molecules are highly organized in a structure known as a crystal. Some of the ways which crystals form are through precipitating from a solution, melt or more rarely deposited directly 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 related to precipitation, although the result is not amorphous or disordered, but a crystal.