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Rare 20.46 carat Okavango Blue Diamond is a unique guest

The 20.46 carat Okavango Blue Diamond, which is one of the most interesting and rare colored diamonds in existence, has been put on public display at the American Museum of National History.

It is believed that this is one of the largest blue diamonds in the world – the size of an almond. The exhibition introduces visitors to scientific lessons regarding its unique origins, especially geology and physics.

“This diamond has an unusual history,” Dr. George Harlow, geologist and curator of AMNH’s Mignone Hall of Gems and Minerals, told

“For most of history, we did not know why diamonds are blue or blue. It was believed that they had little nitrogen. But they actually contain boron, and as soon as there is more boron than nitrogen, the diamond becomes blue or blue.”

Nitrogen is more concentrated in brown and yellow diamonds.

The oval-shaped stone, discovered in 2018 at Botswana’s Orapa mine in the lush Okavango Delta, was graded VVS1 for its near-perfect condition and was cut from a 41.11-carat rough diamond.

Unlike most diamonds, which were formed between 160 and 240 kilometers below the surface, the Okavango blue diamond may have been formed over millions of years in a transition zone—about 640 kilometers below—by a geological process called subduction.

“It’s all about plate tectonics,” Harlow said, noting that boron comes from sea water that “circles inside the earth” over millions of years as oceanic tectonic plates collide and slide under continental plates.

The boron is pushed into the transition zone where it promotes diamond formation.

“Diamonds are a time capsule because they are old, often two billion years or more. They know a lot about our planet,” he added.

The Okavango Blue Diamond was borrowed from the state-owned Okavango Diamond Company and is on display in the museum indefinitely, along with over 1,000 rough diamonds from Botswana. Mining company Okavango Diamond Company controls the sale of 15 percent of diamond products in the country.

Botswana is considered one of the world’s leading producers of high-quality diamonds, accounting for about 80 percent of the country’s exports.

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