Asteroid Impacts Create Deformed Diamonds

Impacts by asteroids and meteorites reportedly create a class of unique, albeit deformed diamonds, shedding light on ancient collisions, including those linked to mass extinction events.

"So-called lonsdaleite is actually the long-familiar cubic form of diamond, but it's full of defects," Péter Németh from Arizona State University (ASU) said in a statement.

Scientists have debated for half a century over the existence of lonsdaleites, a structurally disordered form of ordinary, pristine diamonds, ever since the Canyon Diablo meteorite. This space rock crashed in northern Arizona some 50 years ago and contained a new form of diamond with a hexagonal structure. It was named lonsdaleite, after Dame Kathleen Lonsdale, a famous crystallographer.

Since then scientists have argued that the deformed diamond is evidence of ancient asteroid impacts on Earth, such as the most famous one that wiped out the dinosaurs. But given that pure crystals, even miniscule ones, have never been found or synthesized, the mystery continued to puzzle scientists for years.

So the ASU team decided to re-examine the Canyon Diablo diamonds, as well as investigate lab samples engineered under the very conditions that create lonsdaleites. Advanced electron microscopy revealed that the Canyon Diablo and synthetic samples contained the same structural complexity on a nanometer scale.

"Most crystals have regular repeating structures, much like the bricks in a well-built wall," added researcher Peter Buseck.

"Defects are intermixed with the normal diamond structure, just as if the wall had an occasional half-brick or longer brick or row of bricks that's slightly displaced to one side or another," he said.

These defects in their crystal structure are the result of shock or pressure, making them look unlike ordinary diamonds. And the fact that lonsdaleites are just deformed diamonds, and not a completely separate type of diamond, changes previous scientific studies that treated them as such.

The diamonds are described in the journal Nature Communications.

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