Crystals can be classified into several types based on their internal structure and symmetry. The main categories include cubic, tetragonal, orthorhombic, hexagonal, monoclinic, and triclinic. Each type has a unique arrangement of atoms, which influences the crystal's properties, such as shape and cleavage. Another way to categorize crystals is by their composition. Mineral crystals are formed from natural processes, while synthetic crystals are created in laboratories. Examples of mineral crystals include quartz and calcite, while synthetic options include zirconia and silicon. These classifications help in understanding the diverse characteristics of crystals.