Physics first, Chinese scientists create a rare “hexagonal diamond” that is harder than natural diamonds

Chinese researchers have created what they claim is the first sample of a pure hexagonal diamond. This is theorized to be a rare variant of super-strong diamond found in meteorites from shattered dwarf planets.

Natural diamonds, also known as cubic diamonds, have long been considered the hardest natural material on earth, so much so that the Mohs hardness scale, which evaluates minerals’ resistance to scratches, uses diamonds at the upper end of the scale. It is called cubic diamond because the carbon atoms are arranged in an orderly manner in a cubic structure. In contrast, hexagonal diamonds organize their carbon atoms into a honeycomb-like lattice of hexagons.

elusive mineral

In 1962, researchers at the Pittsburgh Coal Research Center theorized that the layers of carbon atoms that make up diamonds may be organized into a hexagonal lattice rather than a cube, thanks to the way carbon forms bonds with other carbon atoms. In 1967, researchers discovered hexagonal diamond, or lonsdellite, in the lab and wondered if it might be harder than cubic diamond.

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They began looking for it in a special type of diamond-rich meteorite called ureilite, which forms from the shattered mantle of a dwarf planet. The first detection of hexagonal diamonds in the wild was recorded in a 1967 paper. The three Canyon Diablo meteorites (a fragment of an asteroid that formed a large crater in Arizona) have approximately 30% hexagonal diamond facies and 70% cubic diamond facies, and the Goalpara meteorite (found in Assam, India) contains small amounts of hexagonal diamonds.

Not everyone agrees with the existence of Canyon Diablo Lonsdellite. Some scientists believe this evidence can be explained by a chaotic stack of defective cubic diamonds, and were not convinced that previous studies had detected lonsdellite. However, multiple recent studies have identified lonsdellite in meteorites and laboratory samples, including one in 2025 where small amounts of lonsdellite were produced in the laboratory.

The biggest challenge in identifying lonsdellite is the lack of pure samples. It is often mixed with cubic diamond, graphite, and other minerals. This makes it difficult or even impossible to test and measure its unique properties.

The new study, published March 4 in the journal Nature, addressed this problem by creating several pure hexagonal diamond samples about 1.5 millimeters in diameter (large enough to measure the material properties of the samples). The research team found that hexagonal diamond is harder and harder than cubic diamond, and that it is much more resistant to oxidation than cubic diamond. This means hexagonal diamonds can withstand much higher temperatures without reacting with oxygen and becoming sticky on the surface. This is important for applications such as drilling holes.

First evidence of hexagonal diamonds?

This study also provides important evidence that hexagonal diamonds are real materials. “Structural and spectroscopic analyzes supported by large-scale molecular dynamics simulations have clearly confirmed the identity of HD (hexagonal diamond),” the study said.

To create the samples, the researchers compressed highly organized graphite (graphite with tightly arranged carbon atoms) at a pressure of 20 gigapascals, or about 200,000 times Earth’s atmospheric pressure at sea level, for 10 hours and exposed it to temperatures ranging from 2,300 to 3,450 degrees Fahrenheit (1,300 to 1,900 degrees Celsius). At higher temperatures and pressures, lonsdellite began to transform into cubic diamonds.

Hexagonal diamonds have the potential to improve processes and tools that currently rely on cubic diamonds, such as drilling and cutting tools, polishing abrasive coatings, and dissipating heat from electronic equipment. Its presence in a meteorite can tell us a lot about how it formed and where it came from, giving us more clues about our solar system.

Chong-Xin Shan, co-lead of the new Nature study and a physicist at Zhengzhou University, told Nature in an article that this elusive material “has potential applications in many fields, including cutting tools, thermal management materials, and quantum sensing.”

According to the authors, the new study also provides a “practical strategy for producing HD (hexagonal diamond) in bulk,” paving the way for larger samples, more scientific exploration, and industrial applications no longer limited by the hardness of cubic diamonds.