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Scientists find ‘missing ingredient’ for pink diamonds after studying Western Australia’s Argyle mine

Scientists said Tuesday that they have found the “missing ingredient” for pink diamonds, some of the most expensive stones in the world due to their rarity and beauty, and that the discovery could help find more.

More than 90% of all pink diamonds ever found were discovered at the recently closed Argyle mine in remote northwest Australia.

But exactly why Argyle – which unlike most other diamond mines is not in the middle of a continent but on the edge of one – produced so many pink gems remains a mystery.

In a new study published in the journal Nature Communications, a team of Australia-based researchers said pink diamonds were brought to the Earth’s surface by the breakup of the first supercontinent about 1.3 billion years ago.

Hugo Olierook, a researcher at Curtin University and lead author of the study, said two of the three ingredients for forming pink diamonds were already known.

The first ingredient is carbon, and it must be in the bowels of the Earth. Anything less than 150 kilometers deep would be graphite.

The second ingredient is just the right amount of pressure to damage otherwise clear diamonds.

“Push a little and it turns pink. If you press too hard, they turn brown,” she said, noting that most diamonds discovered in Argyle were this less valuable shade of brown.

The missing ingredient was the volcanic event that sent the diamonds to the Earth’s surface, where humans were able to obtain them.

In the 1980s, it was estimated that Argyle diamonds emerged 1.2 billion years ago. But there was no “trigger” for the rare diamonds to emerge at that time, Olierook said, so researchers tried to establish a more precise timeline.

They used a laser thinner than a human hair to probe tiny crystals in a sample of Argyle rock provided by the mine’s owner, mining giant Rio Tinto.

By measuring the age of the elements in the crystals, the researchers determined that Argyle was 1.3 billion years old, meaning diamonds emerged 100 million years later than previously thought.

This coincided with the breakup of the world’s first supercontinent, known as Nuna or Columbia. On Nuna, “almost all of Earth’s landmasses were crushed,” Olierook said.

The Argyle Mine in Kimberly, WA. Photograph: Murray Rayner/Nature Publishing Group/AFP/Getty Images

The immense pressure that transformed the color of diamonds (the second ingredient) occurred during collisions between Western Australia and Northern Australia 1.8 billion years ago.

When Nuna began to break up 500 million years later, the “scar” of that event worsened, Olierook said. Magma shot through this old scar “like a popping champagne cork,” taking the diamonds with it.

Study co-author Luc Doucet said such a “massive explosion” – which sent diamonds traveling at almost the speed of sound – has not taken place in recorded human history.

For the past 200 years, people have searched for diamonds primarily in the centers of large continents. But knowing the “missing ingredient” of pink diamonds could help future efforts to find rare stones, Olierook said, although discovering more is unlikely to be easy or quick.

The ancient mountain belts marking Nuna’s breakup near the edges of continents have the potential to host a new “pink diamond paradise,” he said, naming Canada, Russia, southern Africa and Australia as possible locations.

John Foden, a diamond expert at the University of Adelaide who was not involved in the study, said the researchers had “convincingly demonstrated” the age of the Argyle diamonds. But he warned that other diamond-rich provinces had also been linked to the Nuna breakup and had not produced pink diamonds.

This suggests that “the color pink appears to be a local attribute of Argyle.”

The Argyle mine closed in 2020 due to “various financial reasons,” Olierook said, meaning the value of pink diamonds could continue to rise as supply stagnates.

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