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 says they have confirmed the presence of lonsdaleite, a rare hexagonal form of diamond, in urilite meteorites from the dwarf planet’s mantle.
Lonsdaleite is named after the famous British crystallologist Dame Kathleen Lonsdale, who was the first woman to be elected a Fellow of the Royal Society.
The research team — along with scientists from Monacho University, RMIT University, CSIRO, the Australian Synchrotron, and the University of Plymouth — found evidence of how lonsdaleite formed in urelite meteorites. They published their findings on September 12 in Proceedings of the 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 the crystal structure, is an allotrope of carbon with a hexagonal lattice, as opposed to the cubic lattice of traditional diamond. It is named in honor of Kathleen Lonsdale, a crystallologist.
The team predicted that the hexagonal structure of Lonsdalite atoms makes it more difficult 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 discovered the largest lonsdalite crystals known to date, which are down to a micron in size – much thinner than a human hair.”
According to the research team, lonsdaleite’s unusual structure could help inform new fabrication techniques for superhard materials in mining applications.
What is the origin of these mysterious diamonds?
McCulloch and his team at the Massachusetts Institute of Technology, Ph.D.s. Alan Salk and Dr. Matthew Field, used advanced electron microscopy techniques to capture solid, intact slices of meteorites to create fast snapshots of how ordinary diamonds and diamonds formed.
“There is strong evidence that there is a newly discovered formation process for nesadalites and ordinary diamonds, which is similar to the process of supercritical chemical vapor deposition that occurred in these space rocks, possibly on the dwarf planet shortly after a catastrophic collision,” McCulloch said.
“Chemical vapor deposition is one way that people make diamonds in a lab, primarily by growing them in a specialized room.”
Tomkins said the group suggested that the lonsdaleite in meteorites formed from a supercritical fluid at high temperatures and moderate pressures, almost perfectly preserving the shape and texture of pre-existing graphite.
“Later, Lonsdalite was partially replaced by diamond with the environment cooler and the pressure lower,” said Tomkins, a future fellow at ARC in the School of Earth, Atmosphere and Environment at Monash University.
And so nature has provided us with a process to try and 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 by lonsdaleite. “
Tomkins said the study’s findings helped address a long-standing puzzle regarding the composition of the carbon phases in urelite.
The power of cooperation
Dr Nick Wilson of CSIRO said the collaboration of technology and expertise from the various institutions involved allowed the team to confidently confirm lonsdaleite.
At CSIRO, an electron 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 if taken together – that’s really 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 E.A. 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.
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