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20.46-carat blue diamond on display in New York City

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The trade time period for naturally coloured stones is “fancy,” which makes this uncommon, 20.46-carat Okavango Blue Diamond from Botswana a “fancy deep blue.” But even that may be an understatement for a gem that stands out from 99.98 p.c of all different mined diamonds.

The unusually massive diamond, which was revealed at a brand new exhibit on the American Museum of Natural History in New York City final week, is in regards to the measurement of an almond in its shell. It was doubtless shaped greater than 415 miles underground, beneath part of the inside Earth referred to as the transition zone. The stone surfaced in May 2018 in Botswana’s Orapa mine, and was discovered by the Okavango Diamond Company.

But what’s most instantly placing about this gem is its hue: It will get its azure glow from boron that originated in seawater. Usually, diamonds comprise the next quantity of nitrogen than boron, as a result of nitrogen is extra ample in the setting and boron doesn’t sometimes exist deep in the Earth the place the minerals type. But the Okavango Blue flips the script by containing the next proportion of boron to nitrogen.

[Related: Diamonds contain remnants of Earth’s ancient atmosphere]

So how did aspect no. 5 get fused into this diamond? The ocean incorporates boron, which will get recycled into the bedrock and Earth’s mantle by way of a course of referred to as subduction. When a tectonic plate in the ocean naturally collides with a continental one and slides beneath it, boron will get pushed deeper down into the transition zone. The traces get buried over time, and might finally find yourself in a diamond.

“This is another piece of evidence to support our interpretation of how the planet works,” says George Harlow, a geologist and curator for the American Museum of Natural History’s Halls of Gems and Minerals.

The gem is at the moment on mortgage to the American Museum of Natural History from the federal government of Botswana. Photo: D. Finnin/©AMNH

Scientists have solely discovered about subduction in the previous 50 years, Harlow says, so this theoretical thought behind the Okavango Blue’s formation additional builds on our early understanding of a significant planetary course of. Still, the precise purpose for the diamond’s chemical composition eludes mineralogists. “We don’t really understand why the nitrogen is so low,” says Harlow. Diamonds with increased quantities of nitrogen take on a yellowish shade, so the near-flawless Okavango is a whopper of a discover.

Until the trade comes up with a extra apt time period for such a stellar gem, “fancy” must do for the Okavango Blue.