For the first time, researchers in China have synthetically produced a nearly pure hexagonal diamond, marking a significant breakthrough in materials science.
Long renowned for their exceptional beauty and nearly unmatched hardness, diamonds have been prized as gemstones for use in jewelry and more utilitarian applications in a range of industries.
However, not all diamonds are created equal. Most natural and synthetic diamonds feature a cubic crystal structure, although scientists have long known of a rarer, potentially harder variety possessing a hexagonal form. Although known to occur under rare conditions in nature, the prospect of creating these unique diamond-like structures artificially in the lab has remained controversial.
Now, a synthetic hexagonal diamond has finally been created by a team of researchers from Jilin and Sun Yat-sen Universities in China. The achievement, led by Jilin’s Liu Bingbing and Yao Mingguang, in cooperation with Sun Yat-sen University researcher Zhu Shengcai, marks a major achievement in materials science and identifies a unique structural graphite form.
A Rare and Mysterious Crystal Structure
In the past, a diamond-like six-sided form of carbon, known as lonsdaleite, has been found only under extremely rare conditions in nature. The earliest known discovery of the material occurred during studies of the Canyon Diablo meteorite in 1967. An allotrope of carbon (which causes its hexagonal shape), lonsdaleite is sometimes referred to as a hexagonal diamond, despite this being technically inaccurate since “true” diamonds have a cubic structure.
Although normal diamonds and their hexagonal counterparts are both composed of carbon, the hexagonal variety differs from its common cubic cousins in its unique atomic structure. The difference primarily comes down to how the atoms within each diamond are bonded together.
Cubic diamonds possess a symmetrical configuration with a repeating lattice. This configuration helps give the precious stones their glamorous appearance, although it is also the main factor behind their renowned strength. Given lonsdaleite’s six-sided crystalline structure, it has long been theorized that these unique carbon formations could be even stronger than traditional diamonds.
In the past, replicating the extreme conditions of meteorite impacts that give rise to the natural formation of lonsdaleite has been almost impossible in the lab. Some scientists have even doubted whether the stability of this odd crystal structure would even allow samples to be created artificially, relegating the existence of synthetic lonsdaleite to the realm of theory.
“The synthesis of [hexagonal diamond] remains a challenge and even its existence remains controversial,” the researchers wrote in a recent study detailing their work.
Synthesis Breakthrough: From Graphite to Hexagonal Diamond
That all changed as Bingbing’s research team began their work, first heating a sample of highly compressed graphite—the same type of carbon commonly used in pencil lead.
The team says the result was a “well-crystallized, nearly pure” hexagonal diamond that “is applicable to both bulk and nanosized graphitic precursors.”
Additional experimentation and theoretical analyses also revealed that the post-graphite phase, as the team refers to the sample once converted into a hexagonal diamond (HD), “show that the formation of a post-graphite phase within compressed graphite and temperature gradients promote HD growth.”
“Using this approach, a millimeter-sized, highly oriented HD block comprising stacked single-crystal-like HD nanolayers is obtained,” the team writes in their new paper, confirming their method successfully converted graphite into well-crystallized hexagonal diamond with near-perfect purity.
Extreme Hardness and High-Temperature Stability
One of the team’s most remarkable discoveries is the extreme hardness of the newly synthesized hexagonal diamond, which measured an impressive 155 gigapascals (GPa).
By comparison, conventional cubic diamonds have what scientists call a Vickers hardness rating of between 70 and 150 GPa. This suggests that hexagonal diamonds could outperform their cubic counterparts in wear resistance and durability, confirming past predictions that hexagonal diamonds would be harder than nature’s previously known hardest naturally-occurring materials.
The hexagonal diamond’s unprecedented hardness makes it a promising material for cutting tools and various industrial applications. In addition to its hardness, the hexagonal diamond remained stable while subjected to temperatures of as much as 1,100°C, demonstrating its potential as a next-generation material.
A New Era for Diamond-Based Materials?
Although synthetic diamonds have been produced using high-temperature and high-pressure methods for many decades, as well as methods involving chemical vapor deposition, none have attained the unprecedented strength displayed by the synthetic lonsdaleite created by Bingbing and his team.
Now, having demonstrated that stable synthetic hexagonal diamonds could conceivably be produced in bulk, the team’s discovery has the potential to revolutionize material science with the superior hardness and stability these diamond-like structures can offer. It may also help in the production of ultra-durable coatings and even next-generation semiconductors.
Beyond their industrial uses, successfully producing unique hexagonal diamond-like structures in the lab offers crucial new insights into the behavior of carbon structures under extreme conditions. The team’s findings contribute significantly to our broader understanding of planetary geology and materials engineering through the replication of extreme conditions that produce such substances in nature.
The team acknowledges that hexagonal diamonds remain little more than a laboratory curiosity for now. However, these remarkably strong hexagonal structures will likely find their place in developing cutting-edge technology in the coming years, which the team believes will provide “opportunities for the fabrication and applications of this unique material.”
The team’s discovery was detailed in a new paper, “General approach for synthesizing hexagonal diamond by heating post-graphite phases,” which appeared in the journal Nature on February 10, 2025.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.