Strange hexagonal diamonds may have been ejected into space around 4.5 billion years ago when a dwarf planet collided with a large asteroid. The hexagonal diamonds, also known as lonsdaleite, were discovered in a rare class of meteorites that could have come from the mantle of a dwarf planet, according to new research. Lonsdaleite, like graphite, charcoal, and diamond, is a structural form of carbon. Whereas diamond’s carbon atoms are arranged in a cubic shape, lonsdaleite’s carbon atoms are arranged in hexagons.
“This study proves categorically that lonsdaleite exists in nature,” said Dougal McCulloch, a microscopist at Australia’s RMIT University, in a statement. “We have also discovered the largest lonsdaleite crystals known to date that are up to a micron in size — much, much thinner than a human hair.”
This study proves categorically that lonsdaleite exists in nature. We have also discovered the largest lonsdaleite crystals known to date that are up to a micron in size much, much thinner than a human hair.
Dougal McCulloch
Lonsdaleite was first discovered in the Canyon Diablo meteorite in 1967 and was named after British crystallographer Dame Kathleen Lonsdale. The new research predicts that the hexagonal shape of lonsdaleite makes it harder than regular diamonds with a cubic structure, which might pen new manufacturing techniques to make ultra-hard materials.
The researchers studied lonsdaleite in ureilite meteorites, a rare class of space rocks that scientists think may contain material from the mantle of dwarf planets. The team analyzed slices of these meteorites under the microscope to identify the lonsdaleite and predict its origins, and also studied regularly shaped diamonds found in the rock.
“There’s strong evidence that there’s a newly discovered formation process for the lonsdaleite and regular diamond, which is like a supercritical chemical vapor deposition process that has taken place in these space rocks, probably in the dwarf planet shortly after a catastrophic collision,” McCulloch said. “Chemical vapor deposition is one of the ways that people make diamonds in the lab, essentially by growing them in a specialized chamber.”
Scientists believe that lonsdaleite in meteorites is formed from a supercritical liquid at high temperatures and pressures. The lonsdaleite was able to retain the shape and texture of graphite due to its extreme environment. Lonsdaleite was eventually partially replaced by diamond as the environment cooled and pressure decreased.
The team believes that the industry could replicate the process used to create the unusual mineral.
“Nature has thus provided us with a process to try and replicate in industry,” team leader and geologist Andy Tomkins of Monash University in Australia said in the same statement. “If we can develop an industrial process that promotes the replacement of pre-shaped graphite parts with lonsdaleite, we believe it could be used to make tiny, ultra-hard machine parts.”
