As a unit operation, the term crystallization describes the production of a solid, single-component, crystalline phase from a multicomponent fluid phase. It may be applied to the production of crystalline solids from vapors, melts, or solutions. Crystallization from solution is most important. To complete the preparation of a pure dry solid, it is also necessary to separate the solid from the fluid phase. This is usually carried out by centrifugation or filtration and by drying. The importance of crystallization lies primarily in the purification achieved during the process and in the physical properties of the product. A crystalline powder is easily handled, is stable, and often possesses good flow properties and an attractive appearance.