Weird Hexagonal Diamonds Came From an Asteroid-Dwarf Planet Smashup

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A massive, 50,000-year-old meteorite crater as seen from the air.

Meteor Crater in Arizona. Meteorite fragments from the impact contain lonsdaleite.
Photo: DANIEL SLIM/AFP (Getty Images)

New research indicates that a rare form of diamond may originate in the burbling cores of distant worlds, arriving on Earth thanks to violent cosmic collisions.

According to a team of scientists in Australia, the mineral lonsdaleite—a type of diamond with a hexagonal crystal structure—can be found in meteorites that were likely created when an asteroid collided with a dwarf planet billions of years ago. They investigated 18 ureilite fragments using advanced electron microscopy, to better understand how the lonsdaleite within the space rocks formed. Their research is published today in PNAS.

“This study proves categorically that lonsdaleite exists in nature,” said study co-author Dougal McCulloch, director of the Microscopy and Microanalysis Facility at RMIT in Australia, in a university release.

Lonsdaleite has previously been found in meteorites, including the Diablo Canyon meteorite, a fragment found in Arizona’s famous Meteor Crater. The mineral has also been created in lab settings, but otherwise is vanishingly rare on Earth. The mineral differs from usual diamonds in its crystal structure, which is hexagonal (ordinary diamonds have a cubic crystal structure.) Separate research earlier this year indicated that lonsdaleite’s structure makes it harder than other diamonds.

A mottled grey-brown space rock.

In their recent research, the team found that lonsdaleite occurs naturally in ureilite meteorites, a type of carbon-bearing space rock made up of silicates, sulfides, and metal. They think the recently studied ureilite rocks formed in a the mantle of an ancient dwarf planet, which collided with an asteroid early in the formation of the solar system. The hexagonal lonsdaleite diamonds formed within the ureilite rocks.

Extreme physics tends to bring out uncommon mineral structures. In 1945, the Trinity bomb test showed the effectiveness of the newly developed hydrogen bomb and also created trinitite, a bizarre, glasslike quasicrystal formed from desert sand and copper wiring in the high-pressure, high-temperature environment of the explosion.

An asteroid’s collision with a dwarf planet is a similarly extreme event, one with the high temperatures and pressures necessary to create diamonds. Lonsdaleite has also been found in the meteorite fragments left over from the Meteor Crater impact event, which occurred about 50,000 years ago.

The recent work offers “strong evidence that there’s a newly discovered formation process for the lonsdaleite and regular diamond,” McCulloch added. By the team’s reckoning, the lonsdaleite formed in the ancient dwarf planet “shortly after a catastrophic collision.”

If lonsdaleite’s structure makes it harder than ordinary diamonds, it could have applications in the materials sciences.

“Nature has thus provided us with a process to try and replicate in industry,” said study co-author Andy Tomkins, a geologist at Monash University, in the release. “We think that lonsdaleite could be used to make tiny, ultra-hard machine parts if we can develop an industrial process that promotes replacement of pre-shaped graphite parts by lonsdaleite.”

Certainly, making these diamonds in a lab would be a more efficient method than waiting for the remnants of another cosmic collision to arrive on Earth.

More: Weird New Quantum Diamonds Offer Hope for a Quantum Internet



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