Metaphysics is a major branch of philosophy. It concerns existence and the nature of things that exist. ... The metaphysical idea that reality exists independently of one's mind and yet can be known is called realism. The metaphysical idea that no mind-independent reality exists or can be known is idealism.
A crystal is a solid whose atoms (or molecules) are arranged in a repeating pattern. Crystals are made from fluids by Crystallization, which is a kind of phase change. Usually the fluid is a liquid, but crystals can form from a gas too. ... The surface of crystals often have regions that are flat, called facets.