Crystal's:

          These are solids which have a regular periodic arrangement in their component parties, bounded by flat faces, orderly arranged in reference to one an other, which converge at the edges and vertices. A crystal is symmetrical about its certain elements like points, lines or planes and if it rotated about these elements, it is not possible to distinguish its new position from the original position. This symmetry is an important characteristic based on internal structure of crystal. Symmetry helps one to classify crystals and describing their behavior. At temperatures below that of crystallization, the crystalline state is stable for all solids.

SINGLE CRYSTAL

Most of the materials exist in polycrystalline form, but there are some materials, which exist in the form of single crystals, e.g., sugar, sodium chloride (common salt), diamond, etc.,

Single crystals represent a material in its ideal condition and are produced artificially from their vapor or liquid state. These crystals help us in studying behavior and defects of the material in ideal conditions.