Scientists discover the secret of diamond-bearing meteorites
Scientists discover the secret of diamond-bearing meteorites
Scientists from RMIT and Monash University in Australia have discovered that diamonds formed on an ancient dwarf planet from our solar system.
The planet likely collided with a giant asteroid about 4.5 billion years ago, resulting in high temperatures and moderate pressures.
These conditions caused the graphite in the space rock to undergo a process that turned it into lonsdaleite – a rare hexagonal form of diamond.
This was then partly replaced by ordinary diamond – a tetrahedral lattice of carbon atoms – as the planet cooled and the pressure dropped.
Professor Andy Tomkins, geologist and lead author, said: “Nature has therefore provided us with a process to try to replicate in industry.
“We believe that lonsdaleite could be used to make small, very tough machine parts if we can develop an industrial process that promotes the replacement of pre-formed graphite parts by lonsdaleite,” he added.
Scientists studied 18 samples of ureolite meteorites collected from around the world to verify their origin. Urilites are a rare group of stony meteorites that make up less than one percent of those that fall to Earth.
They contain diamonds of pre-terrestrial origin, some in the form of lonsdaleite.
While regular diamond has carbon atoms in a solid tetrahedral arrangement, the atoms in lonsdaleite are in a hexagonal lattice. No matter how hard it is, ordinary diamonds break and collapse at high enough pressures or if there are small imperfections in the crystal, but this does not happen with lonsdaleite.
The material is named after pioneering British crystallographer Dame Kathleen Lonsdale – the first woman to be elected as a Fellow of the Royal Society.
Its unique structure makes it a harder material than ordinary diamond, predicted Dougal McCulloch, a professor at RMIT.
The researchers used advanced electron microscopy techniques to visualize slices of the meteorite, which revealed how the diamond structures were formed.
The results, published in the Proceedings of the National Academy of Sciences, confirm that lonsdaleite exists in nature.
Professor McCulloch said: “We also discovered the largest lonsdaleite crystals known to date which are down to a micron in size – much thinner than a human hair.”
The results increase understanding of how carbon phases form in ureilite, which has been a long-standing mystery.
They suggest that all ureilite meteorites are remnants of the same primordial planet, and reinforce the theory that today's solar system planets formed from the remains of these early worlds.
The team says the unusual structure of lonsdaleite could help inform new manufacturing techniques for ultra-hard materials in mining applications.
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