Mysterious meteorite could revolutionise industrial diamond manufacturing

A research team, with scientists from Monash University, RMIT University, CSIRO, the Australian Synchrotron and Plymouth University, has confirmed the existence of lonsdaleite, a nano-sized diamond, that could be useful for cutting through ultra-solid materials on mining sites. Lead study author Professor Andy Tomkins, an ARC Future Fellow at Monash University’s School of Earth, Atmosphere and Environment, discovered the unusually formed lonsdaleite crystallites when looking at ureilite meteorites in his lab. Professor Tomkins said it was a case of curiosity-driven science innovation that may lead to great technological advances. “This is exactly the sort of curiosity-piquing observation that sends scientists diving down rabbit holes for months on end,” Professor Tomkins said. The current method for producing industrial diamonds involves chemical vapour deposition, in which diamonds are formed onto a substrate from a gas mix at low pressures. “We propose that lonsdaleite in the meteorites formed from a supercritical fluid at high temperature and moderate pressures, almost perfectly preserving the textures of the pre-existing graphite. Later, lonsdaleite was partially replaced by diamond as the environment cooled and the pressure decreased.” “Nature has thus provided us with a process to try and replicate in industry. We think that lonsdaleite could be used to make tiny, ultra-hard machine parts if we can develop an industrial process that promotes replacement of pre-shaped graphite parts by lonsdaleite.” In this work, the researchers used cutting-edge electron microscopy and synchrotron techniques to create maps of lonsdaleite, diamond, and graphite found in the meteorites. Typically containing larger abundances of diamond than any known rock, ureilite meteorites are arguably the only major suite of samples available from the mantle of a dwarf planet. The parent asteroid was catastrophically disrupted by a giant impact while the mantle was still very hot, creating the ideal conditions for lonsdaleite then diamond growth as the pressure and temperature decreased in a fluid and gas-rich environment. “These findings help address a long-standing mystery regarding the formation of the carbon phases in ureilites that has been the subject of much speculation,” Professor Tomkins said. “And, they offer a novel model for diamond formation in ureilites that settles contradictions in the existing concepts.” RMIT Professor Dougal McCulloch, said the hexagonal structure of lonsdaleite’s atoms made it much harder than regular diamonds, which had a cubic structure. “This study proves categorically that lonsdaleite exists in nature,” said McCulloch, Director of the RMIT Microscopy and Microanalysis Facility. “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.”