This Rare Blue Diamond is Practically a Miracle of Nature

Botswana unveils 'once-in-a-lifetime' 20-carat blue diamond that could become the most expensive in the world 

A remarkable oval shaped blue diamond, weighing over 20 carats, has been unveiled to the world by Okavango Diamond Company (ODC) in Gaborone, Botswana. It is the biggest blue diamond discovery ever made in Botswana. 

The industry term for naturally colored stones is “fancy,” which makes this rare, 20.46-carat Okavango Blue Diamond from Botswana a “fancy deep blue.” But even that might be an understatement for a gem that stands out from 99.98 percent of all other mined diamonds.

At 20.46 carats, the gem is one of the rarest stones in the world, and 'sits in the very top bracket of all-time historical blue diamond finds', the company said in a statement.

Okavango Diamond Company released this picture of a newly-discovered ultra rare blue diamond, weighing over 20 carats

The oval-shaped gem has been named 'The Okavango Blue' in honour of the Okavango Delta, the country's wildlife-rich world heritage site.  The company says the diamond is expected to be sold near the end of the year and could rival the Hope Diamond, which is insured for $250 million. Although the Hope Diamond is larger - at 45.52 carats - the Okavango Blue has the edge on clarity. The Gemological Institute of America graded the Okavango Blue as 'Very, Very Slightly Included,' or VVS2.

It was likely formed more than 415 miles underground, beneath a part of the inner Earth called the transition zone. But what’s most immediately striking about this gem is its hue: It gets its azure glow from boron that originated in seawater. Usually, diamonds contain a higher amount of nitrogen than boron, because nitrogen is more abundant in the environment and boron doesn’t typically exist deep in the Earth where the minerals form. But the Okavango Blue flips the script by containing a higher proportion of boron to nitrogen.

So how did element no. 5 get fused into this diamond? The ocean contains boron, which gets recycled into the bedrock and Earth’s mantle through a process called subduction. When a tectonic plate in the ocean naturally collides with a continental one and slides underneath it, boron gets driven deeper down into the transition zone. The traces get buried over time, and can eventually end up 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.

Scientists have only learned about subduction in the past 50 years, Harlow says, so this theoretical idea behind the Okavango Blue’s formation further builds on our early understanding of a major planetary process. Still, the exact reason for the diamond’s chemical composition eludes mineralogists. “We don’t really understand why the nitrogen is so low,” says Harlow. Diamonds with higher amounts of nitrogen take on a yellowish color, so the near-flawless Okavango is a whopper of a find.