Strange diamonds from an ancient dwarf planet in our solar system may have formed shortly after the dwarf planet’s collision with a large asteroid some 4.5 billion years ago.
A team of scientists said they had confirmed the existence of lonsdaleit, a rare hexagonal form of diamond, in ureilite meteorites from the mantle of an A dwarf planet.
Lonsdaleite is named after the famous British crystallographer, Dame Kathleen Lonsdale, who was the first woman to be elected a Fellow of the Royal Society.
The research team – with scientists from Monash University, RMIT University, CSIROthe Australian synchrotron and Plymouth University – Found evidence of how Lonsdaleit formed in ureilitic meteorites. They published their findings on September 12 in the 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 an allotrope of carbon with a hexagonal lattice, as opposed to the cubic lattice of common 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 Lonsdaleit’s atoms might make it harder than regular diamonds, which would have a cubic structure.
“This study categorically proves that Lonsdaleit occurs in nature,” said McCulloch, director of the RMIT Microscopy and Microanalysis Facility.
“We also discovered the largest Lonsdaleit crystals known to date, measuring up to a micron – much, much thinner than a human hair.”
According to the research team, Lonsdaleit’s unusual structure could help develop new fabrication techniques for ultra-hard materials in mining applications.
What is the origin of these mysterious diamonds?
McCulloch and his RMIT team, graduate student Alan Salek and Dr. Matthew Field used advanced electron microscopy techniques to capture solid and intact slices from the meteorites and create snapshots of how Lonsdaleit and regular diamonds formed.
“There is strong evidence that there is a newly discovered formation process for the Lonsdaleit and regular diamond, which is like a supercritical chemical vapor deposition process that took place in these space rocks, likely on the dwarf planet shortly after a catastrophic collision,” McCulloch said .
“Chemical vapor deposition is one of the ways people create diamonds in the lab, essentially by growing them in a special chamber.”
Tomkins said the group suggested that Lonsdaleit formed in the meteorites from a supercritical fluid at high temperatures and moderate pressures and almost perfectly preserved the shape and texture of the graphite already present.
“Later, Lonsdaleit was partially replaced by diamond as the environment cooled and the pressure decreased,” said Tomkins, an ARC Future Fellow at Monash University’s School of Earth, Atmosphere and Environment.
“So nature has provided us with a process that we can try and replicate in industry. We believe that if we can develop an industrial process that encourages the replacement of preformed graphite parts with Lonsdaleit, Lonsdaleit could be used to manufacture tiny, ultra-hard machine parts.
Tomkins said the study results helped solve a long-standing mystery regarding the formation of the carbon phases in ureilites.
The power of collaboration
dr Nick Wilson said the collaboration of technology and expertise from the various institutions involved has enabled the team to affirm the Lonsdaleite with confidence.
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 collectively it’s really the gold standard,” he said.
References: “Sequential Formation of Lonsdaleite to Diamond in Ureilitic 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.