Crystallite

Crystallites are crystals that do not emerge or the actual crystal form only partially. In the Metallurgy and petrography crystallites are also referred to as a grain.

Crystallites are formed when the crystals solidify in a melt in which they are prevented from surrounding crystals in the free growth. You congeal into a polycrystalline structure with a grain size usually microscopic and are therefore often confused with amorphous solids such as glass. The neighboring crystallites of a polycrystal differ in the orientation of their crystal structure.

On structure micrographs of polished and acid-treated metal or rock samples designated as the grain boundary transitions from one crystallite to the next can be seen as dark lines or color changes.