Science

The “super deep” royal diamonds reveal the mysteries of the earth

The "super deep" royal diamonds reveal the mysteries of the earth
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Smith — a senior research scientist at GIA — examined the diamond for inclusions, chemical clues from our planet’s interior that can show how the crystal was formed and under what conditions. But working with high-quality diamonds is tricky business – it’s usually impossible for researchers to get their hands on the largest specimens. They are sometimes flown around the world to visit potential customers – unfortunately never scientists.

Maya Kopylova, a professor of mineral exploration at the University of British Columbia, says diamond samples are difficult to obtain and most of the diamonds she works with would otherwise have been thrown away. “Researchers need to have a good relationship 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 inch) or larger.”

Even then, acquiring them is complicated and expensive — first, Kopylova must visit the high-security facilities where diamonds are sorted and identify the specimens she wants to examine. Once the acquisition has been approved comes the paperwork – all diamonds must travel with a Kimberley Process certificate, which proves their provenance and helps prevent conflict or “blood” diamonds from entering the market.

However, Smith’s situation is different. At GIA he has access to one of the largest diamond collections in the world – millions of gems sent there for appraisal so they can be insured or sold. “If you want to see something rare and unusual, this is the perfect place because diamonds keep coming through here,” says Smith. “Every few days you could borrow a diamond for maybe a few hours, maybe a day or two and study it.”

A few years earlier, Smith had done just that. Along with an international team of scientists, he casually confiscated 53 of the largest, clearest and most expensive available — including some from the same mine as the Cullinan diamond — and brought them back to his lab to look at under a microscope.

What Smith found was revolutionary. Almost three quarters of the Clippir diamonds contained tiny pockets or “inclusions” of metal that had avoided rusting – something not found in ordinary ones – while the remaining 15 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 the diamonds could have formed no less than 360 km (224 miles) and no more than 750 km (466 miles) underground. In this Goldilocks zone it is deep enough to explain the metal inclusions that have not been exposed to oxygen, which is abundant further up, and it is not so deep that the garnet rocks would have collapsed under the immense pressure of the lower mantle. Ordinary diamonds, on the other hand, only form below the crust 150-200km (93-124 miles) down.

For him Study 2020 — along with Wuyi Wang, GIA’s vice president of research and development — Smith analyzed the 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.

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