High pressures and temperatures within the Earth's crust can change the textures and chemistry of minerals. In some cases, the high temperatures and pressures force traces of water or carbon dioxide out of a mineral, transforming it into a less hydrated species. Sometimes a mineral will not change its chemical composition during metamorphism, but its crystal structure will change into a more compact arrangement. For example, extreme heat and pressure can convert plain carbon from dull graphite, which has a flat, hexagonal crystal structure, to brilliant diamond, which has a closely packed, cubic crystal structure. Scientists say a metamorphic reaction is isochemical if minerals have the same amounts of chemical elements before and after the reaction (iso comes from the Greek word for equal).