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By James Fettes 15 September 2022 2 min read

You’ve probably heard that diamonds are the hardest material on Earth. But what about lonsdaleite diamonds in space?

A team of researchers, including our scientists, have confirmed the existence of the rare hexagonal-structured lonsdaleite diamond. Lonsdaleite appears to be much harder than its more typical cubic cousin.

Researchers found the diamond in samples of ureleite meteorites. The meteorite had broken off the mantle (interior) of a destroyed dwarf planet. A dwarf planet (Pluto is an example) is smaller than a classical planet. The diamond appears to have formed from a catastrophic collision. As temperatures and pressures decreased afterwards, the lonsdaleite replaced existing graphite crystals.

The study, published in Proceedings of the National Academy of Sciences (PNAS), had contributions from us, RMIT University (RMIT), Australian Synchrotron and Plymouth University. Professor Andy Tomkins from Monash University was lead author.

"We think lonsdaleite in the meteorites formed from a supercritical fluid at high temperature and moderate pressures. This almost perfectly preserved the textures of the pre-existing graphite," Andy said.

“Later, lonsdaleite was partially replaced by diamond as the environment cooled and the pressure decreased."

Ureilite cross-section showing lonsdaleite diamond, captured with our electron prob microanalyser (EPMA). Iron in red, magnesium in green, silicon in blue, lonsdaleite in yellow, and diamond in pink.

How do you fold a diamond?

The research team’s work began when Andy was studying ureilite meteorites. These meteorites have an unusually high abundance of diamonds.

Through a microscope, Andy found layered diamonds with distinctive fold patterns. But how do you fold the strongest of minerals?

He turned to a team of our scientists: Dr Nick Wilson, Colin MacRae and Aaron Torpy. Their new fast imaging approach (spectral cathodoluminescence) could find grains of lonsdaleite within a series of meteorites. Our scientists identified grains by its unique spectral signature. This was a critical step. It enabled researchers to discover regions of diamond up to 100 microns.

With the help of researchers from RMIT, the team confirmed the folded diamonds were the elusive lonsdaleite. Additionally, they were the largest lonsdaleite crystallites researchers have discovered to-date.

Shine bright like a diamond

Samples of this size have eluded scientists for decades. It even led some scientists to refute the existence of lonsdaleite diamonds.

This study involved the use of several cutting-edge tools. These included our flagship electron probe microanalyser (EPMA) along with high-resolution transmission electron microscopy (TEM) at RMIT.

Dr Nick Wilson said this collaboration of technology and expertise allowed the team to confirm the lonsdaleite with confidence.

“Individually, each of these techniques is important, but when combined – that’s really the gold standard,” Nick said.

Our researchers Colin MacRae (left), Dr Nick Wilson (middle) and Aaron Tolpy (right) with the flagship electron probe microanalyser (EPMA).

Out of space and into industry

The team’s discovery could lead to the production of new synthetic lonsdaleite. This could be done in much the same way cubic diamonds are grown for use in industries like mining.

If lonsdaleite is indeed much harder than regular diamond, industry could use it create more durable machine parts.

Colin MacRae said lonsdaleite has an added benefit. It appears to require lower pressures than its cubic cousin.

“If something that’s harder than diamond can be manufactured, that’s something industry would want to know about,” Colin said.

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