Super-hard diamonds from a long-extinct dwarf planet could inspire manufacturing techniques | Science | New

Lonsdaleite has been found in so-called “ureilite meteorites”, an unusual type of stony space rock believed to have come from the mantle of a destroyed dwarf planet in the inner solar system. Ureilites tend to contain a relatively high percentage of carbon – around 3% by weight – in the form of graphite and nanodiamonds. The crystals are harder than the regular type of diamond used by jewelers and, if replicated on Earth, could enable the creation of super-tough tools for use in mining.

Professor Tomkins said: “The current method of producing industrial diamonds involves chemical vapor deposition, in which diamonds are formed on a substrate from a low pressure gas mixture.”

The researchers believe that the asteroid responsible for the formation of lonsdaleite would have impacted the host dwarf planet at a time when its mantle was still very hot.

Professor Tomkins added: “We propose that lonsdaleite in meteorites forms from supercritical fluid at high temperature and moderate pressures.”

This, the expert explained, would have almost perfectly preserved the textures of the pre-existing graphite in the fluid.

He said: “Later the lonsdaleite was partially replaced by diamond as the environment cooled and the pressure decreased.”

Professor Tomkins continued: “So nature has provided us with a process to try and replicate in industry.

“We believe that lonsdaleite could be used to make tiny, ultra-hard machine parts if we can develop an industrial process that promotes the replacement of ore-like graphite parts with lonsdaleite.”

In their study, the researchers used state-of-the-art microscopy and synchrotron techniques to create maps of the graphite, lonsdaleite and diamond found in ureilite meteorites.

Ureilites, according to the team, generally contain greater amounts of diamonds than any other known rock.

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The article’s author and physicist, Professor Dougal McCulloch of the Royal Melbourne Institute of Technology (RMIT), explained that it is the hexagonal structure of lonsdaleite that makes it much harder than regular diamonds, whose atoms adopt a cubic structure.

He added: “This study categorically proves that lonsdaleite exists in nature.

“We also discovered the largest lonsdaleite crystals known to date which are down to one micron in size – much, much finer than a human hair.”

The full results of the study have been published in the journal Proceedings of the National Academy of Sciences.

Sarah C. Figueiredo