In 1967 it was discovered that there is a third way of arranging carbon atoms that produces an even harder substance than diamond. The structure is based on graphite’s hexagonal planes but modified to be three-dimensional. This structure, called lonsdaleite, is thought to be 58 percent harder than diamond, although it exists in such small quantities that it is hard to test. The first sample was found in the Canyon Diablo meteorite, where the intense heat and pressure of impact transformed graphite into lonsdaleite.
