Strange diamonds from an ancient dwarf planet in our solar system may have formed shortly after the dwarf planet collided with a large asteroid some 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 crystallographer Dame Kathleen Lonsdale, who was the first female elected member of the Royal Society.
The research team, with scientists from Monash University, RMIT University, CSIRO, Australian Synchrotron and Plymouth University, found evidence of how lonsdaleite formed in ureilite meteorites. They released their results on Sept. 12 in Proceedings of the National Academy of Sciences (PNAS). Monash University geologist Professor Andy Tomkins led the study.
Lonsdaleite, also known as hexagonal diamond in reference to the crystal structure, is a carbon allotrope with a hexagonal lattice, in contrast to the cubic lattice of the conventional diamond. It was named in honor of Kathleen Lonsdale, a crystallographer.
RMIT Professor Dougal McCulloch, one of the senior researchers involved, said the team predicted that the hexagonal structure of the lonsdaleite atoms would potentially make it harder than regular diamonds, which had a cubic structure.
“This study categorically demonstrates that lonsdaleitis 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 finer than a human hair.”
According to the research team, the unusual structure of lonsdaleite could help develop new manufacturing techniques for ultra-hard materials in mining applications.
What is the origin of these mysterious diamonds?
McCulloch and his RMIT team, PhD scholar Alan Salek and Dr. Matthew Field, used advanced electron microscopy techniques to capture solid, intact slices from meteorites to create snapshots of how lonsdaleite and regular diamonds formed.
“There is strong evidence that there is a recently discovered formation process for lonsdaleite and regular diamond, which is like 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, essentially by growing them in a specialized chamber.”
Tomkins said the team proposed that lonsdaleite in meteorites formed from a supercritical fluid at high temperature and moderate pressures, almost perfectly preserving the shape and textures of the pre-existing graphite.
“Later, lonsdaleite was partially replaced by diamond as the environment cooled and the pressure dropped,” said Tomkins, an ARC Future Fellow at Monash University’s School of Earth, Atmosphere and Environment.
“Nature has thus provided us with a process to try and replicate in the industry. We think 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 study’s findings helped address a long-standing mystery related to the formation of carbon phases in ureilites.
The power of collaboration
CSIRO Dr. Nick Wilson said that the collaboration of technology and experience from the various institutions involved allowed the team to confirm lonsdaleitis with confidence.
At CSIRO, an electron probe microanalyzer was used to quickly 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, this really is the gold standard,” he said.
Reference: “Sequential lonsdaleite to diamond formation in ureilite meteorites via on 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 Pintér, Lauren A Jennings and Dougal G. McCulloch, September 12, 2022, Proceedings of the National Academy of Sciences.
DOI: 10.1073 / pnas.2208814119