How do crystals form such perfect geometric shapes?

The answer

Crystals form when atoms, molecules, or ions arrange themselves in a highly ordered, repeating three-dimensional pattern called a crystal lattice. As a substance cools or a solution evaporates, particles settle into the lowest-energy arrangement, which is the most regular and symmetric structure possible. The flat faces and sharp angles of crystals are a macroscopic reflection of this atomic-level order. A single grain of table salt contains about 1.2 quintillion sodium and chloride ions in a perfect cubic lattice.