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Australia Science

The “super-deep” royal diamonds revealing Earth’s secrets

Smith, a senior scientist at the GIA, examined the diamond for inclusions, chemical companions from our planet’s interior that could reveal how the crystal formed and under what conditions. But working with expensive diamonds is not an easy task: usually, researchers cannot get their hands on the largest specimens. Sometimes they are flown all over the world to visit potential clients, but, alas, never scientists.

Maya Kopylova, a professor of mineral exploration at the University of British Columbia, says it’s difficult to get samples of any diamonds, and otherwise most of the diamonds she works with would be discarded. “Researchers have to have good relationships with companies and they will never give you valuable samples,” she says. “So they will never give us diamonds that are 6 mm (0.2 inches) or larger.”

But even so, acquiring them is confusing and expensive – first, Kopylova needs to visit the high-security facilities where the diamonds are sorted and identify the samples she would like to study. Once the purchase is approved, the paperwork begins: all diamonds must be accompanied by a Kimberley Process certificate, which confirms their origin and helps prevent conflict or blood diamonds from entering the market.

However, Smith’s situation is different. At the GIA, he has access to one of the largest diamond collections on the planet – millions of gemstones that have been sent there for appraisal so they can be insured or sold. “If you want to see something rare and out of the ordinary, this is the perfect place because diamonds show up here all the time,” Smith says. “Every few days you can borrow a diamond, maybe for a few hours, maybe a day or two, and study it.”

Smith had done just that a few years earlier. Together with an international team of scientists, he casually requisitioned 53 of the largest, cleanest and most expensive diamonds, including some from the same mines as the Cullinan diamond, and took them to his laboratory to be examined under a microscope.

What Smith discovered was revolutionary. Nearly three-quarters of Clippier diamonds contained tiny pockets or “inclusions” of metal that had escaped rust, which you won’t find in regular diamonds, while the remaining 15 contained a type of garnet that only forms in the Earth’s mantle. layer above its molten core.

Together, these inclusions provide chemical clues that diamonds may have formed at least 360 km (224 miles) and no more than 750 km (466 miles) underfoot. In this Goldilocks zone, it is deep enough to account for the presence of metallic inclusions that have not been exposed to oxygen, which is much higher, and not so deep that garnet rocks collapse under the enormous pressure of the lower mantle. Ordinary diamonds, meanwhile, are mined under the earth’s crust, only 150-200 km (93-124 miles) down.

In his 2020 study — along with Wu Yi Wan, vice president of research and development at GIA — Smith analyzed a 124-carat diamond and found that it formed at the deeper end of the possible range — at least 660 km (410 miles ) below. the surface of the earth.

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