In chemistry and mineralogy, a crystal is a solid in which the element atoms, molecules, or ions are packed in a frequently ordered, repeating pattern extending in all three spatial dimensions.

The word crystal originates from the Greek word κρύσταλλος (krystallos) meaning clear ice, as it was thoughts to be an especially solid form of water. Citation needed: The word once referred mainly to quartz, or "rock crystal".

Most metals encounter in everyday life is polycrystals. [Citation needed] Crystals are often symmetrically intergrown to form crystal twins.