Rare hexagonal diamond formed by crash of dwarf planet and asteroid, scientists believe

'Lonsdaleite' is even harder than normal diamonds and its genesis shows how we might make more

A rare type of diamond that's even stronger than the usual form of the crystal was created when a large asteroid smashed into an ancient dwarf planet 4.5 billion years ago, researchers assert.

This type of diamond is called Lonsdaleite and has a hexagonal crystal structure, unlike the cubic structure found in most diamonds. Scientists believe the hexagonal structure could make Lonsdaleite up to 58 per cent harder than other diamonds.

But studying Lonsdaleite is hard because it isn't easy to make and doesn't form naturally on Earth. Traces of the stuff come from meteorites that have landed on our planet, leading some to question where it came from and how it was formed.

Now, a team of scientists believe they're one step closer to answering those questions. They reckon Lonsdaleite was forged in a collision when a young dwarf planet in the early solar system was pummelled by an asteroid. The impact created the right conditions for the hexagonal diamond to form. 

"There's strong evidence that there's a newly discovered formation process for the Lonsdaleite and regular diamond, which is like a supercritical chemical vapour deposition process that has taken place in these space rocks, probably in the dwarf planet shortly after a catastrophic collision," said Dougal McCulloch, co-author of the paper published in the Proceedings of National Academy of Sciences and a professor interested in microscopy and carbonaceous solids at RMIT University in Australia. 

McCulloch and his colleagues analyzed slices of meteorites containing Lonsdaleite using electron microscopy to determine the right conditions for the material to form. They believe the impact of the collision broke apart the asteroid into meteorite fragments, and Lonsdaleite was created when graphite interacted with a supercritical fluid at high temperatures and moderate pressures.

The graphite crystals in the hot meteorites morphed and organized themselves into a hexagonal structure to create Lonsdaleite. "Later, Lonsdaleite was partially replaced by diamond as the environment cooled and the pressure decreased," said Andrew Tomkins, primary author of the paper and professor at Monash University's School of Earth, Atmosphere and Environment.

The process is similar to chemical vapour deposition, a technique used to create solid state materials that are grown on a substrate in a lab.

If Lonsdaleite can be created on Earth, scientists believe the hard diamond could be used to build mining equipment. "Nature has thus provided us with a process to try and replicate in industry. 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," Tomkins added. 

By examining tiny grains of meteorites the team have also found the largest Lonsdaleite crystals they've observed measure up to a micron - far thinner than a strand of human hair. "This study proves categorically that Lonsdaleite exists in nature," McCulloch concluded. ®

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