“How do we classify crystals that have their periodicity disrupted?”
One of the most fundamental properties of crystals is their periodic structure. However, because of the sheer complexity of the physical universe, a perfect specimen is very rare to obtain. Specifically, the smooth periodicity is often disrupted, and the molecules of crystals will be forced into different grains going in different directions. Because these objects are so common, materials scientists and engineers have decided to term these crystals polycrystals. This interlocking nature makes polycrystals stronger than their monocrystalline counterparts as well as more heat resistant.