Crystals describe the structure of minerals in a solid material. A crystalline structure is when the mineral particles repeat over and over again in a pattern. You may be familiar with minerals such as gold, diamond, topaz and quartz. Many of these minerals are used in jewelry. These minerals and all other minerals have a specific crystal structure as well as other specific properties. You can identify these minerals with properties such as their color, their luster, streak color, hardness, density or crystal system. The crystal structure varies depending on the shape of the crystals. For example, quartz crystals are hexagonal while magnetite crystals are cubic.
Example crystal structure with repeating pattern of particles: