Researchers have discovered the “secret” of the rarity of pink diamonds, which are found almost exclusively in Australia, which explains their astronomical price, according to a study published Tuesday.
More than 90% of all pink diamonds in existence originate from the recently closed Argyle mine in Australia’s North West.
But no one really knew why they were found there, located on the fringe of the southern continent, while most diamond mines are located in the continental environment, such as in South Africa or Russia.
An Australian team explains in the magazine Nature Communications that these rare minerals were formed thanks to the breakup of Earth’s first super-continent, 1.3 billion years ago.
The two “ingredients” needed to make a pink diamond were already known, the first author of the study, Hugo Olierook, of Australia’s Curtin University in Perth, told AFP.
First ingredient, carbon, located at great depth. At less than 150 km depth, this carbon is a common graphite, the kind from which pencil leads are made, and “which doesn’t look very pretty on a wedding ring”, quips the researcher.
Second “ingredient”, colossal pressure, great enough to change the color of a transparent diamond, but without forcing too much.
“Just squeeze a little, it turns pink.” But press just a little more, and 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 to near the surface.
It was initially thought that the Argyle mine had formed 1.2 billion years ago, but it was not clear how the diamonds could have come back, in the absence of 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 at 1.3 billion years ago.
An age corresponding to the fracture suffered by the first super-continent, called indifferently Nuna or Columbia.
Previously “all the land masses were clumped together,” according to Mr. Olierook. The pressure that colored the diamonds arose with the collisions of the Western and Northern Australian land masses 1.8 billion years ago.
This mass fractured 500 million years later, and at this location the magma rose to the surface, carrying the pink diamonds towards the surface, “like a champagne cork”, according to Mr. Olierook.
A “pink diamond paradise”
For 200 years, the quest for diamonds has been concentrated on continental lands, observes the scientist. However, the discovery published Tuesday could reshuffle the cards in this quest.
The mountainous belts resulting from the fracturing of the super-continent Nuna have the potential to become so many “pink diamond paradises”, according to the geologist, who cites potential areas in Canada, Russia, South Africa and Australia.
A conclusion perhaps a little hasty, according to John Foden, diamond expert at the University of Adelaide (south Australia), who did not participate in the study.
This work certainly “convincingly” establishes the age of the Argyle deposit, according to him. And suggest a plausible link between the formation of pink diamonds and the fracturing of Nuna.
However, other sites linked to this geological event have not produced any pink diamonds, he notes. Which could suggest that “the pink character could be an attribute specific to Argyle”.
If this is the case, the price of pink diamonds can only continue to rise, due to a lack of competitors at the mine, which closed in 2020 for economic reasons.