Mysterious diamonds came from outer space, say scientists

Mysterious diamonds came from outer space, say scientists

Professor Andy Tomkins (left) of Monash University with RMIT University PhD scholar Alan Salek and a ureilite meteorite sample. Credit: RMIT University

Rare diamonds from an ancient dwarf planet in our solar system may have formed shortly after the dwarf planet collided with a large asteroid about 4.5 billion years ago, according to scientists.

The research team says they have confirmed the existence of lonsdaleite, a rare hexagonal form of diamond, in ureilite meteorites from the dwarf planet’s mantle.

Lonsdaleite is named after the famous pioneering British crystallographer Dame Kathleen Lonsdale, who was the first woman elected as a Fellow of the Royal Society.

The team, with scientists from Monash University, RMIT University, CSIRO, the Australian Synchrotron and Plymouth University, found evidence of how lonsdaleite formed in ureilite meteorites and published their findings in the Proceedings of the National Academy of Sciences (PNAS). The study was led by geologist Professor Andy Tomkins of Monash University.

One of the lead researchers involved, RMIT professor Dougal McCulloch, said the team predicted that the hexagonal structure of lonsdaleite atoms made them potentially harder than normal diamonds, which had a cubic structure.

“This study categorically demonstrates that lonsdaleite exists in nature,” said McCulloch, Director of RMIT’s Microscopy and Microanalysis Facility.

“We have also discovered the largest lonsdaleite crystals known to date that are down to a micron in size, much, much thinner than a human hair.”

The team says lonsdaleite’s unusual structure could help inform new manufacturing techniques for ultrahard materials in mining applications.

Mysterious diamonds came from outer space, say scientists

Professor Dougal McCulloch (left) and RMIT PhD researcher Alan Salek with Monash University Professor Andy Tomkins (right) at RMIT Microscopy and Microanalysis. Credit: RMIT University

What is the origin of these mysterious diamonds?

McCulloch and his team RMIT, Ph.D. Scholar Alan Salek and Dr. Matthew Field used advanced electron microscopy techniques to capture solid, intact slices of the meteorites to create snapshots of how lonsdaleite and regular diamonds formed.

“There is strong evidence that there is a newly discovered formation process for lonsdaleite and regular diamond, which is like a supercritical process.” chemical vapor deposition process that has taken place in these space rocks, probably in the dwarf planet shortly after a catastrophic collision,” McCulloch said.

“Chemical vapor deposition It’s one of the ways that people make diamonds in the lab, essentially growing them in a specialized chamber.”

Tomkins said the team proposed that the lonsdaleite in the meteorites formed from a supercritical fluid at high temperatures and moderate pressures, almost perfectly preserving the shape and textures of pre-existing graphite.

“Lonsdaleite was later partially replaced by diamond as the environment cooled and pressure decreased,” said Tomkins, an ARC Future Fellow in Monash University’s School of Earth, Atmosphere and Environment.

“So, nature has provided us with a process to test and replicate in industry. We think lonsdaleite could be used to make ultra-hard, tiny machine parts if we can develop a industrial process that promotes the replacement of preformed graphite pieces by lonsdaleite”.

Tomkins said the study’s findings helped address a long-standing mystery about the formation of the carbon phases in ureilites.

“Sequential Lonsdaleite to Diamond Formation in Ureilite Meteorites via In Situ Chemical Fluid/Vapor Deposition” is published in the Proceedings of the National Academy of Sciences (PNAS).


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More information:
Sequential formation of lonsdaleite to diamond in ureilite meteorites through chemical fluid/vapor deposition, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2208814119

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RMIT University


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