The “ultra-deep” royal diamond reveals the secrets of the Earth

Smith—a senior research scientist at GIA—was examining diamonds for impurities, chemical scavengers from within our planet that could reveal how the crystal formed, and under what conditions. But working with high-value diamonds is tricky business—typically, it’s impossible for researchers to get their hands on the largest specimens. They are sometimes flown around the world to visit potential clients – unfortunately, never scientists.

Maya Kopylova, a professor of mineral prospecting at the University of British Columbia, says getting samples of any diamonds is difficult, and otherwise most of the diamonds she works with would have been discarded. “The researchers have to have a good relationship with the companies and they will never give you valuable samples,” she says. “Therefore, they will never give us diamonds of 6 mm (0.2 in) or larger.”

Until then, obtaining them is complicated and expensive – first, Kopylova has to visit the high-security facilities where diamonds are sorted and select the samples that she wants to study. Once the takeover is approved, comes paperwork – all diamonds must travel with a Kimberley Process Certificate, which proves their provenance and helps prevent dispute or “bloody” diamonds from entering the market.

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

A few years ago, that was exactly what Smith did. Together with an international team of scientists, he ordered a display of 53 of the largest, clearest, and most expensive ones available — including some from the same Cullinan diamond mine — and brought them back to his lab for viewing under a microscope.

What Smith found was revolutionary. Roughly three-quarters of Clippir diamonds contained small pockets, or “inclusions” of the rust-avoiding mineral—not something you find in ordinary diamonds—while the remaining fifteen contained a type of garnet that forms only within the Earth’s mantle, the layer above its molten core.

Together, these inclusions provide chemical evidence that diamonds could only have been at least 360 kilometers (224 miles) and no more than 750 kilometers (466 miles) underfoot. In this Goldilocks region, it is deep enough to explain unexposed mineral inclusions, which are abundant on top, and are not so deep that agate rocks can fracture under the enormous pressures of the lower mantle. Meanwhile, ordinary diamonds originate under the crust, only 150-200 kilometers (93-124 miles) deep.

In his 2020 study — along with Wuyi Wang, vice president of research and development at GIA — Smith analyzed the 124-carat diamond and found that it formed at the deeper end of the likely range — at least 660 kilometers (410 miles) below. The earth’s surface.

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