A mineral in which carbon atoms are bonded in a dense tetrahedral lattice; it is the hardest known natural material and is used both as a gemstone and in industrial cutting and grinding tools.
Deep inside Uranus and Neptune, it may rain diamonds. Crushing pressure squeezes hydrocarbons like methane, stripping out carbon that hardens into diamonds and sinks toward the core. In 2017, an X-ray laser that flash-compressed hydrocarbons made diamonds, backing this old idea.