Monash University Professor Andy Tomkins (left) with RMIT University PhD Alan Salek and a sample of the ureilite meteorite. Credit: RMIT University
Strange 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 report that they have confirmed the existence of lonsdaleite, a rare hexagonal form of diamond. dwarf planet.
Lonsdaleite is named after the famous British pioneering crystallographer Dame Kathleen Lonsdale, who was the first woman to be elected a Fellow of the Royal Society.
Research team – with scientists Monash University, RMIT University, CSIROAustralian Synchrotron and University of Plymouth – evidence of how lonsdaleite formed was found in ureilite meteorites. They published their results on September 12 in the journal Proceedings of the National Academy of Sciences (PNAS). Andy Tomkins, professor of geology at Monash University, led the research.
Lonsdaleite, also known as hexagonal diamond due to its crystal structure, is an allotrope of carbon with a hexagonal lattice, unlike the cubic lattice of ordinary diamond. Named after crystallographer Kathleen Lonsdale.
RMIT Professor Dougal McCulloch, one of the lead researchers, said the team predicted the hexagonal arrangement of lonsdaleite atoms made it potentially harder than regular diamonds, which have a cubic structure.
“This study provides conclusive evidence 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, which are down to one micron in size – much, much thinner than a human hair.”
According to the research team, the unusual structure of lonsdaleite could help inform new manufacturing methods for ultra-hard materials in mining applications.
What is the origin of these mysterious diamonds?
McCulloch and his RMIT team, PhD scientist Alan Salek and Dr. Matthew Field used advanced electron microscopy techniques to capture solid and intact slices from meteorites to create snapshots of how lonsdaleite and regular diamonds form.
“There is strong evidence for a newly discovered formation process for lonsdaleite and regular diamond, similar to the supercritical chemical vapor deposition process that occurred in these space rocks, possibly on a dwarf planet shortly after a catastrophic collision,” McCulloch said.
“Chemical vapor deposition is one of the ways people get diamonds in the lab by growing them in a special chamber.”
Professor Dougal McCulloch (left) and PhD scientist Alan Salek from RMIT with Professor Andy Tomkins from Monash University (right) at the RMIT Microscopy and Microanalysis Facility. Credit: RMIT University
Tomkins said the team suggested that the lonsdaleite in the meteorites formed from a supercritical fluid at high temperatures and moderate pressures and preserved the shape and texture of pre-existing graphite almost perfectly.
“Later, as the environment cooled and the pressure decreased, lonsdaleite was partially replaced by diamond,” said Tomkins, an ARC Future Fellow at Monash University’s School of Earth, Atmosphere and Environment.
“So nature provided us with a process to try and replicate in industry. If we can develop an industrial process that promotes the replacement of preformed graphite parts with lonsdaleite, we think lonsdaleite could be used to make small, ultra-hard machine parts.
Tomkins said the results of the study help solve a long-standing mystery about the formation of carbonaceous 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 confirm lonsdaleite with confidence.
At CSIRO, an electron probe microanalyzer was used 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’s really the gold standard,” he said.
Reference: “Through Successive Lonsdaleite to Diamond Formation in Ureilite Meteorites In place 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 Pintér, Lauren A Jennings and Dougal G. McCulloch, 12 September 2022, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2208814119
