An international research team has discovered the enigmatic source of diamonds from space known as lonsdaleite, an extremely rare, hexagonal diamond shape.
Scientists have confirmed the existence of lonsdaleite in ureilite meteorites from the mantle of an ancient dwarf planet in our solar system. The team believes the cosmic diamond formed shortly after the dwarf planet collided with a giant asteroid about 4.5 billion years ago.
The investigation, published in Proceedings of the National Academy of Sciences (PNAS)it included researchers from Monash University, RMIT University, CSIRO, the Australian Synchrotron and the University of Plymouth.
Where does lonsdaleite come from?
Lonsdaleite is named after Dame Kathleen Lonsdale, a famous British female crystallographer who was the first woman to be elected a Fellow of the Royal Society.
For their research, the team used advanced electron microscopy techniques to obtain hard, intact sections of the meteorites to develop snapshots of how lonsdaleite and ordinary diamonds form.
RMIT’s Professor Dougal McCulloch, one of the project’s senior researchers, commented: “There is strong evidence that there is a newly discovered formation process for lonsdaleite and ordinary diamond that is like a supercritical vapor deposition process that happened in this space rocks, possibly in the dwarf planet shortly after a catastrophic collision. Chemical deposition is one way people make diamonds in the lab, basically by growing them in a specialized chamber.
“This research conclusively proves that lonsdaleite exists in nature. We also found the largest lonsdaleite crystals known to date, which are down to a micron in size – much, much thinner than a human hair.
The researchers hypothesized that the lonsdaleite in the meteorites formed from a supercritical fluid at high temperature and moderate pressure, which preserved almost perfectly the shape and textures of the preexisting graphite.
Professor Andy Tomkins, head of the study and a geologist at Monash University, said: “Later, lonsdaleite was partially replaced by diamond as the environment cooled and the pressure decreased. In this way, nature has provided us with a process to try and reproduce in industry.”
Potential applications of space diamond
The team explained that the hexagonal structure of lonsdaleite atoms makes it harder than ordinary diamonds, which have a cubic structure. Therefore, their robust structure may make them useful for new manufacturing techniques for ultrahard materials in mining applications.
Professor Tomkins concluded: “We think that lonsdaleite can be used to make small, ultra-hard machine parts if we can develop an industrial process that promotes the replacement of pre-formed graphite parts with lonsdaleite.”