March 14, 2026
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New claim to create elusive ‘hexagonal’ diamond is strongest yet
After decades of debate, scientists say they have found the clearest evidence yet for this rare form of carbon
Conventional diamond, called cubic diamond, is known as the hardest substance in the world. But researchers think hexagonal diamond may be more difficult.
Diamond is known as the hardest mineral on earth. But researchers have pursued an unusual variant of it – known as hexagonal diamond – which may be even more difficult. After decades of claims and counterclaims about whether this mysterious material can be synthesized in a lab, scientists in China report that they have.
Researchers covet the material because it “has potential applications in many fields, such as in cutting tools, in thermal control materials and in quantum recording,” says Chongxin Shan, a physicist at Zhengzhou University who led the work.
“There are hundreds of claims from people who think they’ve seen it,” says Oliver Tschauner, a mineralogical crystallographer at the University of Nevada, Las Vegas, who has peer-reviewed the paper. “But this is the first very precise characterization of this elusive material.”
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Shock value
Conventional diamond consists entirely of carbon atoms arranged in tetrahedra, which ultimately form a cubic crystal structure. Viewed from a certain angle, this lattice of atoms looks like a stacked series of stretched honeycomb layers. Each successive layer is slightly offset from its neighbors, in a pattern that repeats every third layer. But in 1962, scientists predicted that diamond could adopt a different structure—one with hexagonal features—where the pattern repeats every other layer.
In conventional or cubic diamond, the carbon bonds between the layers are marginally weaker than those within the layers, limiting the diamond’s strength. In the hexagonal form, the bonds between the layers are shorter and stronger than those in cubic diamond, and predictions suggest that these features should make hexagonal diamond more than 50% harder.
In 1967, scientists reported finding hexagonal diamond in a meteorite found in Arizona, which was part of the space rock that created the iconic nearby Meteor Crater. The team suggested that the shock of the impact had transformed graphite in the meteorite into hexagonal diamond, naming this new mineral lonsdaleite, after pioneering crystallographer Kathleen Lonsdale.
Around the same time, a separate research team said they had produced hexagonal diamond in the laboratory by heating and compressing graphite. But some researchers have cast doubt on this report. And others argued that lonsdaleite was not hexagonal diamond at all; they said it was just cubic diamond with multiple defects.
Peak demand
Much of the debate stems from the X-ray diffraction experiments used to discern the material’s crystal structure, explains Tschauner. In this type of experiment, when X-rays are scattered through a crystal, some of them combine and produce peaks in the X-ray intensity that reveal the positions of the atoms. However, the pattern of diffraction peaks obtained from highly defective cubic diamond will closely mimic hexagonal diamond, says Tschauner. To reliably demonstrate the hexagonal structure, some additional telltale peaks must be present. “This new paper shows these peaks,” he says. “That’s why I think so.”
Shan and his colleagues started with highly oriented pyrolytic graphite, then sandwiched it between anvils made of tungsten carbide under 20 gigapascals of pressure (200,000 times atmospheric pressure) at 1,300–1,900 °C to produce millimeter-sized samples of hexagonal diamond. Tests showed that the material was stiffer, more resistant to oxidation and slightly harder than cubic diamond.
Last year, another research group independently reported making hexagonal diamond. “It looks like the new paper is very similar to ours. I have to say, I can’t see any difference,” said Ho-kwang Mao, a physicist who is director of the Shanghai Advanced Research in Physical Sciences center in China and who led the team involved in the 2025 paper. “But we are pleased that they have reproduced our results.”
Hex sign
“It’s almost the same,” says Tschauner, pointing out that the X-ray analysis by Mao and his colleagues was missing one or two of the diffraction peaks expected to be seen in hexagonal diamond. A third group also reported in 2025 that they had created “almost pure” hexagonal diamond that was harder than cubic diamond.
Mao says that tiny traces of cubic diamond that contaminated the samples produced by both his group and Shan’s may explain why their hexagonal diamond is not as difficult as predicted. “If we can get rid of all that, we can probably make it even harder,” he says.
Taken together, these papers should be enough to convince hexagonal diamond skeptics that the material exists and can be made in the lab, says Shan.
The work could also revive the search for true hexagonal diamond in meteorites, Tschauner says, because it proves the material can be created by pressures and temperatures consistent with meteor impacts. “I think we need to find out if it actually exists in nature,” he says. “For meteorite research, the quest now is to find it.”
This article is reproduced with permission and var first published March 4, 2026.
