Crystals are solid substances in which the individual atoms, molecules, or ions that make up the material are arranged in an ordered and repeating pattern. The regularity and symmetry of the arrangement form planes and angles that give the crystal a distinct geometric shape. Crystals can form naturally within rocks or through the condensation of molecules in a solution. Some crystals form when minerals in a liquid solution form crystals around a surface and eventually form a solid. Crystals can also be made in a lab as a part of chemical syntheses and purifications. When exposed to light, some crystals can emit light of different colors. Many crystals also exhibit photoluminescence properties. Crystals have a variety of uses, from electronics to aesthetics. They can be used to make jewelry and decorate homes. Crystals are also used in medicine, electronics, and other industries.