The ordered internal structure of large crystals, like these spinels, is reflected in their geometric shapes.
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.