Mysterious diamonds formed after a dwarf planet collided with large asteroid about 4.5 billion years ago

An international team of scientists have confirmed the existence of lonsdaleite, a rare hexagonal form of diamond, in ureilite meteorites from inside an ancient dwarf planet. The researchers say that these mysterious diamonds may have formed shortly after the dwarf planet collided with a large asteroid about 4.5 billion years ago.

The team predicted the hexagonal structure of lonsdaleite's atoms made it potentially harder compared to regular diamonds with a cubic structure, according to Professor Dougal McCulloch from RMIT University, who is one of the senior researchers involved in the study.

"This study proves categorically that lonsdaleite exists in nature," said McCulloch, Director of the RMIT Microscopy and Microanalysis Facility.

McCulloch and his RMIT team, PhD scholar Alan Salek and Dr Matthew Field, used advanced electron microscopy techniques to capture solid and intact slices from the meteorites to create snapshots of how lonsdaleite and regular diamonds formed.

The team proposed that lonsdaleite in the 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 decreased, said geologist Professor Andy Tomkins, an ARC Future Fellow at Monash University's School of Earth, Atmosphere and Environment and the lead author of this study.

The researchers say that the unusual structure of lonsdaleite could help inform new manufacturing techniques for ultra-hard materials in mining applications.

The team, which also includes scientists from Monash University, CSIRO, the Australian Synchrotron and Plymouth University, has published their findings in the Proceedings of the National Academy of Sciences (PNAS) journal.