Scientists Are Making ‘Super-Diamonds’ Harder Than Any Mineral on Earth
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First identified in 1967, lonsdaleite is the hardest naturally-occuring mineral ever discovered—yes, it’s even harder than diamonds.
Lonsdaleite, however, has only been found in meteorites, suggesting it requires intense heat and pressure to form.
In a new study, scientists have taken a huge step forward in perfecting the method to synthesize lonsdaleite, which could lead to multiple scientific breakthroughs.
Diamond is the hardest mineral on Earth. This fact would likely pass muster at your local trivia night, but scientists suspect there’s more to the geologic story.
Diamond is a carbon allotrope, meaning it’s a type of carbon that exists in another form due to its environment (in this case, a lot of time and pressure). Charcoal and graphite are also allotropes of carbon. However, there’s another allotrope—first identified in 1967 when scientists examining a meteorite in Canyon Diablo, Arizona—known today as lonsdaleite. Named for the Irish crystallographer Dame Kathleen Lonsdale, lonsdaleite’s most shocking attribute is that it’s even harder than diamond, because while diamond forms with a tetrahedral arrangement in its carbon lattice (known as diamond cubic), lonsdaleite forms a hexagonal one that increases thermal stability and hardness.
As you might expect, first finding lonsdaleite on a meteor means this mineral isn’t naturally occurring on Earth. That’s because it requires more extreme geologic pressures to form than the Earth can provide. A study in 2022 confirmed that lonsdaleite likely forms from “shock compressions” and high temperatures created during a meteor’s impact with Earth, transforming graphite into this ultra-hard mineral. While this dashed hopes for finding a large, naturally-occurring vein of this potentially useful super-diamond, it did reinforce the idea that lonsdaleite could be effectively manufactured.
Now, a team of researchers have improved upon existing methods for making lonsdaleite. In the past, synthesized production of lonsdaleite often produced a lot of graphite and diamonds in the process, but this new research optimizes the method for producing these hexagonal diamonds (HD) significantly. The results of the study were published in the journal Nature Materials.
“With potentially superior mechanical properties and an intriguing structure, lonsdaleite has also received intense research interest in materials science,” the authors wrote. “Nearly pure bulk HD has been obtained in well-designed experiments by applying high pressure and high temperature with a temperature gradient.”
The process required a very deft ability to apply pressure and temperature while aligning graphite stacks just so—a process known as Bernal-stacking, or AB-stacking—to keep the layers from sliding.
“To overcome such unfavorable factors for HD growth, we synthesized HD from graphite via intermediate post-graphite phases in which interlayer bonding may lock a near-AB stacking in the compressed graphite and hinder the further sliding of layers during high-temperature stimulation, favoring the formation of HD,” the authors wrote. “Both our experiments and simulations indicate that, besides the formation of the post-graphite phase, the presence of a temperature gradient is also critical for HD synthesis.”
While this is far from an industrial scale process, producing lonsdaleite lab in a will give scientists greater insight into the conditions needed for its rare natural formation, as well as potential advancements in exotic materials (such as superconductors) that can make use of its unique properties.
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