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 of our solar system.
It is possible that the planet 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 transformed it into lonsdaleite - a rare hexagonal form of diamond.
This was then partially replaced by ordinary diamond - a tetrahedral network of carbon atoms - as the planet cooled and the pressure decreased.
Professor Andy Tomkins, geologist and lead author, said: “Nature has therefore given us a process to try to replicate in industry.
"We believe that lonsdaleite can be used to make very tough small machine parts if we can develop an industrial process that promotes the replacement of preformed graphite parts with lonsdaleite."
Scientists studied 18 samples of urilite meteorites collected from around the world to verify their origin. The urelites are a rare group of stony meteorites that make up less than one percent of those that fall to Earth.
It contains diamonds of pre-earth origin, some in the form of lonsdaleite.
While ordinary diamond contains carbon atoms in a solid tetrahedral arrangement, the atoms in lonsdaleite are in a hexagonal lattice. No matter how hard it is, ordinary diamonds will break and collapse at high enough pressures or if there are small defects in the crystal, but this does not happen with lonsdaleite.
The substance is named after the pioneering British crystallologist Dame Kathleen Lonsdale - the first woman to be elected a Fellow of the Royal Society.
Dougal McCulloch, a professor at RMIT, predicts that its unique structure makes it a much tougher material than regular diamond.
The researchers used advanced electron microscopy techniques to visualize the meteorite slices that revealed how 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 crystal known to date, which is up to a micron in size - much thinner than a human hair."
The results add to the understanding of how the carbon phases of urelites form, which has been a longstanding mystery.
They suggest that all urelites are remnants of the same primordial planet, and support the theory that the planets of today's solar system formed from the remnants of these early worlds.
The team says that lonsdaleite's unusual structure could help inform new fabrication techniques for superhard materials in mining applications.
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