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.
A team of scientists claims to have confirmed the existence of lonsdaleite, a rare hexagonal form of diamond, in ureilite meteorites from the mantle of a dwarf planet.
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 research 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. They published their findings on September 12 in the Proceedings of the National Academy of Sciences (PNAS). Geologist Professor Andy Tomkins of Monash University led the study.
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 conventional diamond. It was named in honor of Kathleen Lonsdale, a crystallographer.
RMIT Professor Dougal McCulloch, one of the lead researchers involved, 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.”
According to the research team, the unusual structure of lonsdaleite could help inform new techniques for manufacturing ultra-hard materials in mining applications.
What is the origin of these mysterious diamonds?
McCulloch and his RMIT team, PhD student Alan Salek and Dr. Matthew Field, used advanced electron microscopy techniques to capture solid, intact slices of the meteorites to create snapshots of the formation of lonsdaleite and regular diamonds.
“There is strong evidence that there is a newly discovered formation process for lonsdaleite and ordinary diamond, which resembles a supercritical chemical vapor deposition process that took place in these space rocks, probably on 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 group proposed that 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 that lonsdaleite could be used to make tiny, ultra-hard machine parts if we can develop an industrial process that promotes the replacement of preformed graphite parts with lonsdaleite.
Tomkins said the results of the study helped solve a long-standing mystery regarding the formation of carbon phases in ureilites.
The power of collaboration
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 electron probe microanalyzer was used to rapidly map the relative distribution of graphite, diamond, and lonsdaleite in the 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: “Sequential Diamond Lonsdaleite Formation in Ureilite Meteorites via On the site Chemical Fluid/Vapor Deposition” 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 Pinter, Lauren A Jennings and Dougal G. McCulloch, September 12, 2022, Proceedings of the National Academy of Sciences.
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