Mysterious Diamonds Came From Outer Space, Scientists Say

Mysterious Diamonds Came From Outer Space, Scientists Say

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

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

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

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

The team, made up of scientists from Monash University, RMIT University, CSIRO, the Australian Synchrotron and the University of Plymouth, found evidence of lonsdaleite formation in ureilite meteorites and published his 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 it potentially harder than regular diamonds, which had a cubic structure.

“This study is categorical proof that lonsdaleite exists in nature,” said McCulloch, director of the RMIT Microscopy and Microanalysis Facility.

“We also discovered the largest lonsdaleite crystals known to date, up to a micron in size – much, much finer than a human hair.”

The team says the unusual structure of lonsdaleite could help inform new techniques for making ultra-hard materials in mining applications.

Mysterious Diamonds Came From Outer Space, Scientists Say

RMIT Professor Dougal McCulloch (left) and PhD student 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. Researcher Alan Salek and Dr. Matthew Field used advanced electron microscopy techniques to capture solid, intact slices of meteorites to create snapshots of the formation of lonsdaleite and diamonds regular.

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

“Chemical vapor deposition is one of the ways people make diamonds in the lab, basically by growing them in a specialized chamber.”

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

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

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

Tomkins said the study results helped solve a long-standing mystery about the formation of 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 diamond lonsdaleite in ureilite meteorites by 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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