Researchers have discovered the “secret” to the rarity of pink diamonds, which are found almost exclusively in Australia, which explains their astronomical price, according to a study published on Tuesday.
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More than 90% of all pink diamonds in existence come from the recently closed Argyle mine in northwest Australia.
But no one really knew why they were found there, on the edge of the southern continent, while most diamond mines are in continental environments, such as South Africa or Russia.
An Australian team explains in the journal Nature Communications that these rare minerals were formed by the breakup of Earth’s first supercontinent 1.3 billion years ago.
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The two “ingredients” needed to make a pink diamond are already known, the study’s first author, Hugo Olierook from Australia’s Curtin University in Perth, told AFP.
The first component, carbon, is found at great depths. At less than 150 km deep, this carbon is common graphite, used to make pencil leads, and “which doesn’t look particularly nice on a wedding ring,” the researcher jokes.
Second “ingredient”, enormous pressure, large enough to change the color of a transparent diamond but without applying too much pressure.
“Just press a little, it will turn pink. But if you press a little more, it turns brown,” explains the geologist.
“Champagne cork”
The Australian team’s discovery helps explain what caused pink diamonds to burst from the Earth’s crust close to the surface.
The Argyle Mine was originally thought to have formed 1.2 billion years ago, but it was not clear how the diamonds could have returned without an associated geological phenomenon.
The researchers then refined the dating of the deposit by measuring the age of tiny crystal elements in a rock from the mine. And arrived 1.3 billion years ago.
An age corresponding to the rupture suffered by the first supercontinent, indifferently called Nuna or Columbia.
Previously, “all the landmasses were clustered together,” Mr. Olierook said. The pressure that colored the diamonds came from the collisions of the landmasses of western and northern Australia 1.8 billion years ago.
That mass shattered 500 million years later, at which point the magma rose to the surface, pulling the pink diamonds to the surface “like a champagne cork,” Mr. Olierook said.
A “Pink Diamond Paradise”
The scientist observes that the search for diamonds has been concentrated on continental areas for 200 years. However, the discovery published on Tuesday could reshuffle the cards in this quest.
The mountain belts formed by the splitting of the Nuna supercontinent have the potential to become so many “pink diamond paradises,” according to the geologist, who names potential areas in Canada, Russia, South Africa and Australia.
A perhaps somewhat hasty conclusion, according to John Foden, a diamond expert at the University of Adelaide, South Australia, who was not involved in the study.
In his opinion, this work certainly “convincingly” establishes the age of the Argyle deposit. And suggest a plausible connection between the formation of pink diamonds and the rupture of Nuna.
However, other sites associated with this geological event have not produced pink diamonds, he notes. Which could suggest that “the pink mark could be a specific attribute of Argyle.”
If this is the case, the price of pink diamonds can only continue to rise due to a lack of competitors in the mine, which closed in 2020 for economic reasons.