Extra-hard hexagonal diamonds can now be grown in a lab

Hexagonal diamond up to 60 per cent stronger than normal diamonds could be used to create super-tough drilling and cutting tools for industrial applications

By Matthew Sparkes

30 July 2025

The crystal structure of hexagonal diamond

ogwen/Shutterstock

A harder form of diamond that has eluded scientists for decades can now be synthesised in the laboratory, and could be used to make extremely tough cutting and drilling tools.

Diamonds as we know them have a cubic arrangement of atoms in their crystalline structure. But for at least 60 years, we have been aware of another form – hexagonal diamond – that is much tougher, thanks to its crystals having no uniform shear lines along which breaks can propagate.

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Natural hexagonal diamond occurs in meteorites, where it is known by the mineral name lonsdaleite, but only in mixtures with cubic diamond. Previous attempts to synthesise hexagonal diamonds have yielded only tiny traces that are similarly impure.

Now, Ho-Kwang Mao at the Center for High Pressure Science and Technology Advanced Research in Beijing and his colleagues have succeeded in creating a relatively large sample of hexagonal diamond that is 1 millimetre in diameter and 70 micrometres thick, with purity close to 100 per cent.

While normal diamond has been synthesised for some time, the researchers explored a range of pressures and temperatures to find a sweet spot in which hexagonal diamonds were produced. This ended up being 1400°C at 20 gigapascals – 200,000 times the atmospheric pressure on Earth.