What Is a Crystal?

A crystal consists of matter that is formed from an ordered arrangement of atoms, molecules, or ions. Because there are repeated units, crystals have recognizable structures. There are seven systems of crystal structures, which are also called lattices or space lattices.

Examples of everyday materials you encounter as crystals are table salt (sodium chloride or halite crystals), sugar (sucrose), and snow. Many gemstones are crystals, including quartz and diamond.