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

Scientists said on Tuesday they have found the “missing ingredient” for pink diamonds – some of the world’s most expensive stones due their rarity and beauty – and the discovery could help find more.

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

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

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

Hugo Olierook, a researcher at Curtin University and the study’s lead author, 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 Earth. Anything shallower than 150km deep would be graphite

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

“Push just a little bit and it turns pink. Push a little too hard and they turn brown,” he said, noting that most of the diamonds discovered at Argyle were of this less valuable brown hue.

The missing ingredient was the volcanic event that sent the diamonds shooting up to the Earth’s surface, where humans could get their hands on them.

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

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

By measuring the age of elements in the crystals, the researchers determined that Argyle was 1.3bn years old – meaning the diamonds came up 100m years later than previously thought.

That lined up with the breakup of the world’s first supercontinent, known as Nuna or Columbia. In Nuna, “just about every single landmass on Earth was squashed together”, Olierook said.

The immense pressure that twisted colour into the diamonds – the second ingredient – occurred during collisions between western Australia and northern Australia 1.8bn years ago.

When Nuna started to break up 500m years later, it reaggravated the “scar” from that event, Olierook said. Magma shot up through this old scar “like a champagne cork going off”, taking the diamonds along for the ride.

The study’s coauthor, Luc Doucet, said such a “massive explosion” – which sent the diamonds travelling at near the speed of sound – has not taken place in recorded human history.

Over the last 200 years, people have mostly looked for diamonds in the centre of massive continents. But knowing the “missing ingredient” for pink diamonds could assist future efforts to find the rare stones, Olierook said – though discovering more was unlikely to be easy or quick.

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

John Foden, an expert on diamonds at the University of Adelaide who was not involved in the study, said the researchers had “convincingly shown” the age of the Argyle diamonds. But he cautioned that other diamond-rich provinces had also been linked to Nuna’s break-up – and they had not produced pink diamonds.

This suggests that “pinkness seems to be a local Argyle attribute”.

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 stalls.