Structurally, materials are divided into amorphous and crystalline, although liquid crystals and quasi-crystals also occur in nature. The science that studies the laws within crystals, their internal structure and their appearance is called crystallography. Crystals are formed by the solidification of liquid metal, and during solidification the atoms in the interior take on a specific arrangement known as a crystal lattice. Miller's indices are used to determine the distance of atoms within the lattice from the origin point or to determine the area within the lattice. If crystalline things crystallize under different conditions, such as temperature, pressure, etc., and have the same chemical composition, then polymorphism occurs. To determine the very structure of the crystal, its chemical composition or physical properties, the method of X-ray diffraction, better known as X-rays, is used. Depending on the irregularity within the crystal structure itself, materials can have deteriorated or improved properties. Due to the fact that all crystals have a solid structure, crystallography as a science is closely related to other scientific fields, such as mineralogy, metallurgy, biology, mathematics, etc. To all these sciences, crystallography gives more than it receives in return, therefore it can be said that crystallography is one of the starting points in a large number of industrial activities.