China team grows world's rarest millimeter-sized ‘hexagonal’ diamond

Chinese researchers have successfully synthesized millimeter-sized, pure-phase hexagonal diamonds (lonsdaleite), a rare carbon form previously found only in tiny amounts at meteorite impact sites. Unlike common cubic diamonds, hexagonal diamonds have a six-sided atomic structure with shorter, stronger bonds between layers, theoretically making them up to 50% harder. Using a high-pressure, high-temperature method, the team from Zhengzhou University created these crystals by compressing graphite at 20 gigapascals and heating it to nearly 3,500°F. Characterization through X-ray diffraction and atomic-scale microscopy confirmed the purity and structure of the hexagonal diamonds. Tests revealed they are stiffer and more oxidation-resistant than cubic diamonds, though only slightly harder than predicted, suggesting a need to revise theoretical models of carbon hardness. This breakthrough holds promise for industrial applications such as cutting tools, thermal management, and quantum sensing, as well as providing geologists with a valuable marker for studying meteorite impacts and planetary histories. The