A team of researchers has reported the first laboratory synthesis and recovery of bulk hexagonal diamond, a crystal form long predicted to be harder than the conventional gems used in cutting tools and jewelry. The claim, published in Nature, stands as the strongest evidence yet for a material whose very existence has been questioned for more than a decade. If the results hold up under independent scrutiny, the work could settle one of materials science’s most persistent disputes and open new possibilities in industrial applications and planetary research.
A Diamond With a Different Architecture
Conventional diamond, called cubic diamond, is known as one of the hardest substances in the world. Its carbon atoms form a cubic crystal structure, an arrangement that gives it extraordinary rigidity. But researchers have long theorized that carbon could also arrange itself into a hexagonal crystal structure, producing a variant often called lonsdaleite or hexagonal diamond. Theoretical models suggest this hexagonal form could exceed cubic diamond in hardness, a property that would make it valuable for drilling, machining, and protective coatings.
The new study describes the creation of macroscopic crystals under high-pressure, high-temperature conditions. According to the paper, the team assigned the material a crystallographic space group and performed direct measurements of its mechanical properties. What sets this work apart from earlier attempts is the reported purity, size, and depth of characterization, according to a Nature news analysis that called it the strongest such claim to date. By moving beyond nanoscale grains and mixed phases, the researchers argue that they have finally isolated hexagonal diamond as a bulk material.
Decades of Doubt Over Lonsdaleite
The controversy traces back to the 1960s, when scientists first identified what they believed was hexagonal diamond in meteorite fragments. For decades, researchers reported finding the material in ureilite meteorites, a class of space rocks rich in carbon. But in 2014, a study in Nature Communications directly challenged the field, arguing that supposed hexagonal domains in meteorites were actually faulted and twinned cubic diamond rather than a genuinely distinct hexagonal phase. The authors went further, contending that lonsdaleite does not exist as a discrete material at all.
That conclusion divided the community. Some researchers accepted it as a corrective to decades of overinterpretation, seeing many prior claims as resting on ambiguous diffraction patterns and limited imaging. Others pushed back, pointing to experimental data they said could not be explained by faulted cubic structures alone. A formal reply published in the Proceedings of the National Academy of Sciences directly addressed criticisms from Nemeth and Garvie, laying out criteria for recognizing a true hexagonal phase in ureilites and presenting specific contested observations that the authors argued supported lonsdaleite.
The dispute was not just semantic. If lonsdaleite were merely a defective form of cubic diamond, then claims about its superior hardness and its role as a geological marker would be on shaky ground. If, however, a distinct hexagonal lattice existed in nature, it would imply unique formation pathways and potentially different physical behavior under extreme conditions.
Shock Waves and Meteor Craters
Running parallel to the meteorite debate, experimental physicists have tried to create hexagonal diamond in the laboratory by mimicking the violent conditions of asteroid impacts. In 2016, researchers used in situ shock-compression experiments to show that graphite can transform into a hexagonal phase on nanosecond time scales when pressures exceed specific thresholds. Those experiments, conducted with powerful lasers and fast diagnostics, suggested that lonsdaleite could form directly from graphite during impact-like events.
Lawrence Livermore National Laboratory highlighted that work, noting that hexagonal diamond might flag ancient collisions on planetary surfaces. If confirmed, the presence of this phase in rocks could help planetary scientists identify and date impact structures on Earth and other worlds, adding a new tool to the study of planetary evolution.
Separately, Washington State University researchers documented the transformation of graphite into hexagonal diamond at what they described as lower pressures than earlier work, publishing their results in a peer-reviewed paper in Science Advances. These shock-physics experiments, conducted by multiple independent groups, built a body of evidence that hexagonal diamond could form under dynamic compression, even as skeptics maintained that the resulting material was structurally indistinguishable from defective cubic diamond.
Access to detailed data from these experiments has also improved. Materials scientists now routinely consult supplementary datasets from shock studies to compare diffraction signatures and phase diagrams, looking for consistent fingerprints of a hexagonal lattice.
Why the New Claim Carries More Weight
Previous reports of hexagonal diamond suffered from a common problem: the samples were tiny, impure, or poorly characterized, leaving room for critics to argue that researchers were misidentifying faulted cubic structures. The new work differs on all three counts. According to the Nature study, the team produced bulk, macroscopic crystals and performed extensive crystallographic analysis to confirm a hexagonal structure. Direct mechanical property measurements were also reported, a step that earlier studies rarely achieved with sufficient rigor.
This matters because the central question in the debate has always been one of evidence quality. Critics who argued that lonsdaleite does not exist as a discrete material pointed to overlapping diffraction peaks, complex twinning, and nanoscale domains that defy clear structural assignment. If the new crystals are large enough and pure enough for independent labs to reproduce the measurements, the dispute could finally move from interpretation of blurry data to direct comparison of well-characterized specimens.
Replication will be crucial. Other groups will need to verify the reported space group, confirm the absence of cubic inclusions, and test whether the mechanical properties truly exceed those of conventional diamond. Even modest differences in hardness or fracture toughness could have outsized implications for industrial uses, but only if they are robust across synthesis batches and measurement techniques.
The Meteorite Connection Still Divides Researchers
Even if the laboratory synthesis is confirmed, the question of whether hexagonal diamond exists naturally in meteorites remains open. A 2022 study proposed a formation pathway in ureilites involving lonsdaleite and diamond, suggesting the material forms via in situ chemical fluid or vapor deposition rather than direct impact compression. That model, if correct, would mean hexagonal diamond plays a role in the thermal and chemical history of certain meteorite parent bodies, not just in the instant of collision.
Skeptics counter that the observational signatures used to identify lonsdaleite in natural samples can also be produced by stacking faults in ordinary cubic diamond. The 2014 paper that denied lonsdaleite’s existence has not been retracted, and its authors have not yet publicly responded to the new bulk synthesis. Until they do, the meteorite side of the debate will likely remain unresolved, even as laboratory evidence strengthens.
In practice, resolving the natural-occurrence question will likely require applying the same high standards used in the new synthesis study to extraterrestrial samples: larger volumes, cleaner separations of phases, and multimodal characterization that combines diffraction, imaging, and spectroscopy. Only then can researchers determine whether the hexagonal lattice found in the lab truly matches any structures in space rocks.
What a Harder Diamond Could Change
If hexagonal diamond is confirmed to be intrinsically harder or more wear-resistant than cubic diamond, the most immediate impact would be in cutting and drilling technologies. Industrial diamond is already used in saw blades, drill bits, and machining tools; a tougher variant could extend tool lifetimes, reduce downtime, and enable work on even more abrasive materials. That, in turn, could lower costs for mining, construction, and advanced manufacturing.
Protective coatings are another promising avenue. Thin films of a harder diamond phase on vulnerable components (such as turbine blades, bearings, or spacecraft parts) could improve resistance to erosion and micrometeoroid impacts. Because hexagonal and cubic diamond are both forms of carbon, engineers might be able to adapt existing chemical vapor deposition processes, provided the right pressure–temperature conditions can be achieved or approximated.
Beyond industry, the new material could become a powerful probe of extreme physics. Diamonds are already used as anvils to generate enormous pressures in the laboratory. If hexagonal diamond proves both harder and more resilient, it could push the limits of what diamond-anvil cells can achieve, opening windows onto the behavior of matter deep inside planets and stars.
For planetary science, bulk hexagonal diamond offers a reference point that has long been missing. With a well-characterized phase in hand, researchers can compare laboratory spectra and diffraction patterns directly with signals from meteorites and impact structures. Whether or not lonsdaleite turns out to be common in nature, the ability to synthesize and study it at scale marks a turning point in a debate that has spanned more than half a century.
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*This article was researched with the help of AI, with human editors creating the final content.
