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Sunday, December 04, 2022

Scientists say this mysterious diamond came from outer space

Professor Andy Tomkins (left) from Monash University with RMIT PhD scientist Alan Salk and a urilite meteorite sample. Credit: RMIT University

Exotic 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.

A team of scientists say they have confirmed the presence of lonsdaleite, a rare hexagonal form of diamond, in urelite meteorites from the mantle. dwarf planet.

Lonsdaleite is named after the renowned British crystal expert Dame Kathleen Lonsdale, who was the first woman to be elected a Member of the Royal Society.

The research team – with scientists from Monash University and RMIT. University and CSIRO Synchrotron Australia, and the University of Plymouth – I found evidence of how lonsdaleite formed in urelite meteorites. They published their findings on September 12 in Prosiding National Academy of Sciences (PNAS). The study was led by geologist Professor Andy Tomkins of Monash University.

Lonsdaleite, also known as hexagonal diamond in reference to its crystal structure, is an allotrope of carbon with a hexagonal lattice, as opposed to the traditional cubic lattice of diamond. Named in honor of Kathleen Lonsdale, a crystal expert.

The team estimates that Lonsdalite’s atomic hexagonal structure 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 proves that Lonsdalite exists in nature,” said McCulloch, director of the Microscopy and Microanalysis Facility at RMIT.

“We also found the largest lonsdalite crystal known to date, which is up to one micron in size – much thinner than a human hair.”

According to the research team, the unusual structure of lonsdaleite could help inform new fabrication techniques for superhard materials in mining applications.

What is the origin of this mysterious diamond?

McCulloch and his team at the Massachusetts Institute of Technology, Ph.Ds Alan Salk and Dr. Matthew Field, used state-of-the-art electron microscopy techniques to capture solid, intact slices of meteorites to create quick snapshots of how diamonds and ordinary diamonds form.

“There is strong evidence that there was a formation process for the newly discovered nesadalite and ordinary diamond, which is similar to the supercritical chemical vapor deposition process that occurs in these space rocks, possibly on a dwarf planet shortly after the cataclysmic collision,” McCulloch said.

“Chemical vapor deposition is one of the ways people make diamonds in the laboratory, especially by growing them in special rooms.”

Dougal Mcculloch, Alan Salk And Andy Tomkins

Professor Dougal McCulloch (left) and PhD researcher Alan Salk of RMIT with Professor Andy Tomkins of Monash University (right) at RMIT’s Microscopy and Microanalysis Facility. Credit: RMIT University

Tomkins said the group suggested that the lonsdaleite in meteorites formed from supercritical fluids at high temperatures and moderate pressures, retaining almost perfectly the shape and texture of pre-existing graphite.

“Then, Lonsdalite was partially replaced by diamond with a cooler environment and lower pressure,” said Tomkins, a prospective fellow at ARC in the School of Earth, Atmosphere and Environment at Monash University.

And nature has given us processes to try and replicate in industry. We believe that lonsdaleite can be used to make extra-rigid machine parts if we can develop industrial processes that encourage replacement of lonsdaleite’s preformed graphite parts. “

Tomkins said the research findings help address a longstanding puzzle about the composition of the carbon phase in urelite.

The power of collaboration

Dr Nick Wilson from CSIRO said the technology collaboration and experience from the various institutions involved allowed the team to confidently confirm lonsdaleite.

At CSIRO, electron probe microanalysis is used to rapidly map the relative distribution of graphite, diamond and Lonsdalite in samples.

“Individually, each of these techniques gives us a good idea of ​​what this substance is, but put together – it really is the gold standard,” he said.

Reference: “Lonsdaleite sequencing of diamond formation in the Ureilite Meteorite via In place Chemical liquid/vapour deposition” by Andrew J. Tomkins, Nicholas C. Wilson, Colin McRae, Alan Salk, Matthew R. Field, Helen E. Brand, Andrew D. Langendam, Natasha R. Stephen, Aaron Turbie, Zanett Pinter, and Lauren A. Jennings and Dougal G. McCulloch, 12 Sep 2022, Available here. Prosiding National Academy of Sciences.
DOI: 10.1073/pnas.2208814119

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