Diamond

The hardest known natural material, diamond is pure carbon arranged in an isometric crystal structure, sitting at the top of the Mohs scale at hardness 10. It forms deep in the Earth's mantle under extreme pressure and temperature and reaches the surface through volcanic kimberlite pipes. Crystals are typically octahedral or cubic, transparent, and adamantine, with perfect octahedral cleavage and a specific gravity of 3.50 to 3.53. Colors span colorless, yellow, brown, blue, green, and pink. Beyond its role as a gemstone, diamond's hardness underpins its extensive industrial use in cutting and abrasive tools. Its perfect octahedral cleavage, exploited by gem cutters, coexists with a hardness that resists abrasion from every other substance.

Diamond is the hardest known natural material, composed of pure carbon arranged in an isometric crystal structure. Formed deep in Earth's mantle under extreme pressure and temperature, diamonds are brought to the surface by volcanic eruptions through kimberlite pipes.