Mysterious diamonds found on Earth came from outer space

Stones' hexagonal structure makes them harder then regular diamonds

Monash University Professor Andy Tomkins, left, with Royal Melbourne Institute of Technology PhD student Alan Salek study a ureilite meteor sample at an RMIT facility in Melbourne, Australia. Photo: RMIT University

Images of graphite, lonsdaleite, and diamond in ureilites. Photo: RMIT university

Prof Dougal McCulloch, left, Mr Salek from RMIT and Mr Tomkins from Monash, right, look at computer images of the meteor samples. Photo: RMIT University

An uncut 1,109-carat diamond named 'Lesedi La Rona' at Sotheby's auction house in London. AFP

Scientists have confirmed that a mysterious type of diamond found on Earth came from outer space.

New research shows that the strange diamonds, which are believed to be much harder than diamonds found on Earth, came from an ancient dwarf planet in our solar system.

Scientists studied 18 samples of ureilite meteorites – rare type of stony meteorite with a unique mineralogical composition – found in Australia and North Africa, some of which contained the diamonds.

In lonsdaleite diamonds, the atoms have a hexagonal structure, instead of a cubic structure as in regular diamonds, which is what possibly makes them harder.

The study, published in the Proceedings of National Academy of Sciences journal on Monday, was led by scientists from Monash University, Royal Melbourne Institute of Technology University (RMIT), the Australian Synchrotron and Plymouth University and the Commonwealth Scientific and Industrial Research Organisation, an Australian government agency for scientific research.

“This study proves categorically that lonsdaleite [hexagonal diamond] exists in nature,” said Dougal McCulloch, director of the RMIT microscopy and microanalysis facility.

“We have also discovered the largest lonsdaleite crystals known to date that are up to a micron in size ― much, much thinner than a human hair.”

The researchers believe that the diamonds may have formed shortly after the dwarf planet collided with a large asteroid about 4.5 billion years ago.

Of the 18 ureilites examined, all contained graphite, most had a diamond and a small number had lonsdaleite.

The team used advanced electron microscopy techniques to capture solid and intact slices from the meteorites.

This helped create snapshots of how lonsdaleite and regular diamonds formed.

“There’s strong evidence that there’s a newly discovered formation process for the lonsdaleite and regular diamond, which is like a supercritical chemical vapour deposition process that has taken place in these space rocks, probably in the dwarf planet shortly after a catastrophic collision,” Prof McCulloch said.

“Chemical vapour deposition is one of the ways that people make diamonds in the lab, essentially by growing them in a specialised chamber.”

It is believed that the unusual structure of lonsdaleite could help create new manufacturing techniques for ultra-hard materials in mining.

Cubic diamonds on Earth were formed more than three billion years ago deep within the Earth’s crust.

When intense heat and pressure cause carbon atoms to crystallise, diamonds form.

They are found at a depth of about 150 to 200 kilometres below the surface of Earth.

There is ongoing research on whether these diamonds may also form elsewhere in space when asteroids collide, pushing carbon inside to form these crystals.

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