China Synthesizes Bulk Hexagonal Diamond, Potentially Harder Than Natural Diamond

In a groundbreaking achievement, researchers in China have successfully synthesized millimetre-scale samples of pure hexagonal diamond, a rare and theorized variant of diamond found in meteorites. This breakthrough, published March 4 in the journal Nature, resolves a decades-long debate about the existence and properties of this superhard material and opens doors for potential applications across various industries.

The Elusive Hexagonal Diamond: Lonsdaleite

Natural diamond, or cubic diamond, is renowned as the hardest naturally occurring material, serving as the upper limit on the Mohs hardness scale. Hexagonal diamond, also known as lonsdaleite, differs in its atomic structure. While cubic diamond arranges carbon atoms in a cubic lattice, hexagonal diamond organizes them in a honeycomb-like hexagonal lattice. Theorized in 1962 by researchers at the Pittsburg Coal Research Center, lonsdaleite was first detected in meteorites in 1967, specifically in Canyon Diablo meteorites from Arizona and Goalpara meteorites from India [1].

Decades of Debate and the Challenge of Purity

For sixty years, the existence of lonsdaleite was questioned. Some scientists attributed anomalous diffraction signals to flawed cubic diamond with chaotic stacking, rather than a distinct hexagonal structure [4]. The primary obstacle to definitive confirmation was the lack of pure samples. lonsdaleite typically occurs mixed with cubic diamond, graphite, and other minerals, making accurate property testing impossible.

Breakthrough Synthesis and Confirmed Properties

The Zhengzhou University team overcame this challenge by creating several hexagonal diamond samples approximately 0.06 inches (1.5 millimeters) in diameter. These samples were synthesized by compressing highly organized graphite at 20 gigapascals (around 200,000 times Earth’s atmospheric pressure) and heating it to temperatures between 2,300 and 3,450 degrees Fahrenheit (1,300 to 1,900 degrees Celsius) [1]. The researchers found that hexagonal diamond is both stiffer and harder than cubic diamond, and exhibits greater resistance to oxidation [2]. This enhanced oxidation resistance means it can withstand higher temperatures without surface degradation, a crucial property for applications like drilling.

Implications and Potential Applications

The successful synthesis of bulk hexagonal diamond validates theoretical predictions and opens up a range of potential applications. These include improved cutting and drilling tools, more effective polishing abrasive coatings, and enhanced thermal management for electronics [3]. The presence of hexagonal diamond in meteorites provides valuable insights into the formation and origins of these celestial bodies.

“The elusive material “has potential applications in many fields, for example in cutting tools, in thermal management materials and in quantum sensing”,” stated Chong-Xin Shan, co-lead of the study and a physicist at Zhengzhou University [3].

The research team’s method provides a “practical strategy for producing HD (hexagonal diamond) in bulk form,” paving the way for larger samples, further scientific investigation, and industrial applications that surpass the limitations of cubic diamond [Lai, S., Yang, X., Shi, J., Liu, S., Guo, Y., Yan, L., Zang, J., Zhang, Z., Jia, Q., Sun, J., Cheng, S., & Shan, C. (2026). Bulk hexagonal diamond. Nature.].