Researchers in China say they have produced hexagonal diamond, a long-disputed form of carbon that theory predicts could be substantially harder than ordinary diamond. In a report described by Scientific American, drawing on coverage first published in Nature, a team led by physicist Chongxin Shan at Zhengzhou University reports the clearest evidence yet that the material can be synthesized in a laboratory. Predictions suggest hexagonal diamond should be more than 50% harder than conventional diamond, though the samples made so far fall short of that mark.
Why hexagonal diamond has been so contested
Ordinary diamond, known as cubic diamond, is built entirely from carbon atoms arranged into tetrahedra that stack into a cubic crystal. Viewed from a certain angle, the lattice looks like buckled honeycomb layers, each offset slightly from its neighbor in a pattern that repeats every three layers. In 1962, researchers predicted that diamond could take a different form, with the pattern repeating every two layers, giving it hexagonal features.
The appeal is structural. In cubic diamond, the bonds between layers are slightly weaker than those within layers, which limits the crystal’s strength. In the hexagonal form, the bonds between layers are shorter and stronger, and that difference is what leads to the prediction that hexagonal diamond should be markedly harder.
The material also has a history tangled up with meteorites. In 1967, researchers reported finding hexagonal diamond in a meteorite tied to the impact that formed Meteor Crater in Arizona, and named the mineral lonsdaleite after crystallographer Kathleen Lonsdale. But the claim was contested for decades. Some scientists doubted that lab attempts had really produced the material, and others argued that lonsdaleite was not hexagonal diamond at all, but cubic diamond riddled with defects.
How the new samples were made and checked
Shan and his colleagues started with highly oriented pyrolytic graphite and squeezed it between anvils made of tungsten carbide, applying 20 gigapascals of pressure, roughly 200,000 times atmospheric pressure, at temperatures between 1,300 and 1,900 degrees Celsius. The process yielded millimeter-sized samples. Tests indicated the material was stiffer, more resistant to oxidation, and slightly harder than cubic diamond.
The key to the claim is the crystal analysis. Much of the historical debate came down to X-ray diffraction, in which scattered X-rays combine to produce intensity peaks that reveal where atoms sit. The problem is that highly defective cubic diamond can produce a pattern that closely mimics hexagonal diamond. To prove the hexagonal structure conclusively, a few extra telltale peaks must appear. Oliver Tschauner, a mineralogical crystallographer at the University of Nevada, Las Vegas who peer-reviewed the paper, said the new work shows those peaks. “That’s why I believe it,” he said, calling it the first very accurate characterization of the elusive material.
The result does not stand entirely alone. Another group led by physicist Ho-kwang Mao independently reported making hexagonal diamond in 2025, and a third group reported making “nearly pure” hexagonal diamond harder than cubic diamond the same year. Tschauner noted that the earlier X-ray analyses lacked one or two of the diffraction peaks expected in hexagonal diamond, which is part of why the newest paper is being read as the strongest case so far.
What it means and what is still unknown
If the material holds up to scrutiny, the potential uses are practical. Shan pointed to applications in cutting tools, thermal management materials, and quantum sensing, all areas where an even harder or more durable form of carbon would be valuable. Taken together with the 2025 papers, the new results should be enough to convince skeptics that hexagonal diamond exists and can be made in a lab, Shan said.
Several things remain open. The synthesized material has not reached the more-than-50% hardness gain that theory predicts. Mao suggested that tiny traces of cubic diamond contaminating the samples could explain the shortfall, and said that removing them might make the material harder still. Whether genuine hexagonal diamond also exists in nature is unsettled; Tschauner said the lab work, by showing the material can form at pressures and temperatures consistent with meteor impacts, should reinvigorate the search for it in meteorites.
For readers, the takeaway is measured. This is a strong new claim in a field defined by decades of claims and counterclaims, and it rests on the kind of detailed crystal fingerprint that earlier reports lacked. The practical payoff, a working superhard material for tools or sensors, would still require making it in larger, purer quantities, and that work has not yet been done.
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*This article was researched with the help of AI, with human editors creating the final content.
