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

A strange diamond 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 says they have confirmed the presence of lonsdaleite, a rare hexagonal diamond, in ureilite meteorites from the dwarf’s mantle.

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

The research team, along with scientists from Monash University, RMIT University, CSIRO, the Australian Synchrotron, and the University of Plymouth, have found evidence of how lonsdaleite formed in ureilite meteorites. They announced their findings on September 12th. Proceedings of the National Academy of Sciences (PNAS). Professor Andy Tomkins, a geologist at Monash University, led the study.

RMIT professor Dougal McCulloch, one of the senior researchers involved, said the team predicted that the hexagonal structure of lonsdaleite’s atoms could be harder than regular diamond, which had a cubic structure. said.

“This study clearly demonstrates that lonsdaleite exists in nature,” said McCulloch, director of the RMIT Microscopy and Microanalytical Facility.

“We also found the largest lonsdaleite crystals known to date, up to 1 micron in size, much thinner than a human hair.”

According to the research team, lonsdaleite’s unusual structure could help inform new manufacturing techniques for ultra-hard materials in mining applications.

What is the origin of these mysterious diamonds?

McCulloch and his RMIT team, PhD scholars Alan Salek and Dr. Matthew Field, used advanced electron microscopy techniques to capture solid, intact slices from meteorites to determine how lonsdaleite and ordinary diamond are. I created a snapshot of how it was formed.

“There is strong evidence for the newly discovered process of formation of lonsdaleite and ordinary diamonds. This is due to the supercritical chemical vapor deposition that occurred on these cosmic rocks, possibly dwarf planets shortly after their catastrophic impact. It’s kind of a process,” McCulloch said. .

“Chemical vapor deposition is one way to make diamond in the lab, basically by growing it in a special chamber.”

RMIT Professor Dougal McCulloch (left) with PhD Scholar Alan Salek and Monash University Professor Andy Tomkins (right) at the RMIT Microscopy and Microanalytical Facility.Credit: RMIT University

According to Tomkins, the group proposed that lonsdaleite in meteorites formed from supercritical fluids at high temperatures and moderate pressures, preserving the shape and texture of existing graphite almost perfectly.

“Later, as the environment cooled and the pressure dropped, the lonsdaleite was partially replaced by diamond,” says Tomkins, an ARC Future Fellow in the Department of Global and Atmospheric Environments at Monash University.

“Nature has thus provided us with a process to try and replicate in industry. We believe we can use it to produce small, ultra-hard mechanical parts.”

Tomkins says the findings helped address a long-standing mystery about the formation of ureilite’s carbon phase.

the power of collaboration

CSIRO’s Dr. Nick Wilson said the combination of technology and expertise from the various agencies involved has allowed the team to confidently identify Lonsdaylight.

CSIRO used an electron probe microanalyzer to rapidly map the relative distribution of graphite, diamond, and lonsdaleite in samples.

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

Reference: “Continuous formation of lonsdaleite to diamond in ureirite meteorites” there By Andrew G. Tomkins, Nicholas C. Wilson, Colin MacRae, Alan Salek, Matthew R. Field, Helen EA Brand, Andrew D. Langendam, Natasha R. Stephen, Aaron Torpy, Zsanett Pintér, Lauren A Jennings and Dougal G. McCulloch , 12 September 2022, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2208814119