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).

Have you eaten any minerals lately? Almost certainly! Halite is the formal name of the mineral we use as table salt. Humans use salt not just to season food, but also to cure (preserve) meats. Clay minerals, part of the silicate group, serve as mild abrasives in toothpaste, while the fluoride comes from the mineral fluorite. Finely ground silicon dioxide is an anti-caking agent in many powdered foods such as gravy mixes and non-dairy coffee "creamer." The mineral trona is the primary source of sodium carbonate, which helps baked goods rise and gives toothpaste that foamy feeling in your mouth. Calcium sulfate from the mineral gypsum coagulates (or solidifies) tofu, a soybean-based food. Many of the plants we eat depend on mineral-based fertilizers for robust growth.