Monash University Professor Andy Tomkins (left) with RMIT PhD scientist Alan Salk and a urilite meteorite sample. Credit: RMIT University
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Exotic diamonds from an ancient dwarf planet in our solar system may have formed shortly after the dwarf planet collided with a large asteroid some 4.5 billion years ago.
A team of scientists say they have confirmed the presence of lonsdaleite, a rare hexagonal form of diamond, in the mantle’s urelite meteorites. dwarf planet.
Lonsdaleite is named after the famous British crystallologist Dame Kathleen Lonsdale, who was the first woman to be elected a member of the Royal Society.
Research group – with scientists from Monash UniversityAnd RMIT UniversityAnd CSIROthe Australian synchrotron e University of Plymouth Evidence has been found of how lonsdaleite formed in urelite meteorites. They released their results on 12 September a Proceedings of the National Academy of Sciences (PNAS). The study was led by Monash University geologist Professor Andy Tomkins.
Lonsdaleite, also known as hexagonal diamond in reference to the crystal structure, is a carbon allotrope with a hexagonal lattice, as opposed to the cubic lattice of the traditional diamond. It is named in honor of Kathleen Lonsdale, a crystallologist.
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The team predicted that the hexagonal structure of Lonsdalite’s atoms makes it harder than regular diamond, which has a cubic structure, said RMIT professor Dougal McCulloch, one of the senior researchers involved.
“This study conclusively demonstrates that Lonsdalite exists in nature,” said McCulloch, director of the Microscopy and Microanalysis Facility at RMIT.
“We also discovered the largest lonsdalite crystals known to date, which are down to one micron in size, much thinner than a human hair.”
According to the research team, the unusual structure of lonsdaleite could help develop new fabrication techniques for superhard materials in mining applications.
What is the origin of these mysterious diamonds?
McCulloch and his Massachusetts Institute of Technology team, PhD students Alan Salk and Dr. Matthew Field, used advanced electron microscopy techniques to capture solid, intact slices of meteorites to create quick snapshots of how ordinary diamonds and diamonds formed.
“There is strong evidence that there is a recently discovered formation process for nesadalite and ordinary diamonds, which is similar to the supercritical chemical vapor deposition process that occurred in these space rocks, possibly on the dwarf planet shortly after a catastrophic collision,” McCulloch said.
“Chemical vapor deposition is one way people make diamonds in a laboratory, mainly by growing them in a specialized room.”
Professor Dougal McCulloch (left) and RMIT PhD researcher Alan Salk with Professor Andy Tomkins of Monash University (right) at RMIT’s Microscopy and Microanalysis Facility. Credit: RMIT University
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Tomkins said the team suggested that lonsdaleite in meteorites formed from a supercritical fluid at high temperatures and moderate pressures, almost perfectly preserving the shape and texture of the pre-existing graphite.
“Later, Lonsdalite was partially replaced by diamond with the cooler environment and lower pressure,” said Tomkins, a prospective ARC fellow at Monash University’s School of Earth, Atmosphere and Environment.
And so nature has given us a process to try to replicate in industry. We believe lonsdaleite can be used to make extra-rigid machine parts if we can develop an industrial process that promotes the replacement of preformed graphite parts with lonsdaleite. “
Tomkins said the study’s findings helped solve a long-standing conundrum related to the phase composition of carbon in urelite.
The power of cooperation
CSIRO’s Dr Nick Wilson said the collaboration of technology and expertise from the various institutions involved allowed the team to confidently confirm lonsdaleitis.
At CSIRO, an electronic probe microanalyzer was used to quickly map the relative distribution of graphite, diamond and Lonsdalite in the samples.
“Individually, each of these techniques gives us a good idea of what this substance is, but when taken together, this really is the gold standard,” he said.
Reference: “Sequenced Lonsdaleite Diamond Formation in Ureilite Meteorites via On site Chemical fluid / vapor deposition “by Andrew J. Tomkins, Nicholas C. Wilson, Colin McRae, Alan Salk, Matthew R. Field, Helen EA Brand, Andrew de Langendam, Natasha R. Stephen, Aaron Turbie, Zanett Pinter, Lauren A Jennings and Dougal G. McCulloch, September 12, 2022, Available here. Proceedings of the National Academy of Sciences.
DOI: 10.1073 / pnas.2208814119
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