Structures with perfect symmetries govern the physics of solid matter. Order in nature has always mesmerized us, so much that, in the ancient times, it was deemed a sign of divine design. As our understanding of nature progressed, rational explanations replaced the old supernatural beliefs. Today we know that atoms in a solid arrange in an ordered lattice that minimizes the energy cost. Wonderful crystalline patterns arise that determine the properties of the whole material, such as its transparency and its hardness.