Nuclei grow to form crystals – grain structure. It is important to have knowledge about the types of imperfections that exist and the roles they play in affecting the behavior of materials. Point defects. Any irregularity in the pattern of crystal arrangement in a solid lattice is called imperfection in solids — Imperfections in Crystalline Solids Wei Cai, William D. Nix Index More Information Nuclei form. Solidification result of casting of molten materialsteps. Defect: deviations from the idea