IN THE ROUGH

The best diamonds in the world are buried at the bottom of the Atlantic Ocean

The best diamonds in the world come from the sea. Swept up from riverbeds by the mighty Orange River in southern Africa back when dinosaurs still roamed the earth, their bumpy journey to the Atlantic polished them and broke up any stones with flaws, ensuring only the strongest and best survived.

Those diamonds landed off the coast of what is now Namibia, creating the world’s richest marine-diamond deposit. The country’s territorial waters are now estimated to hold 80 million carats, and the world’s biggest diamond miner, De Beers, has quietly built up an armada off the coast to vacuum up those precious gems.

Diamonds on land are running out; no economically viable new source has been found in 20 years. Mines in Canada and Australia could run out in five years, analysts say, and Botswana, home to De Beers’ sales headquarters, will be bare by 2030. Business consultancy Bain has predicted that even with bountiful sources like Russia and Namibia, the global supply of rough diamonds will decline by 2% per year until 2030.

Men look at pile of uncut diamonds
A pile of uncut diamonds in 1955 Oranjemund, Namibia. Debmarine sorts its diamonds in the same town today. (Volkmar K. Wentzel, National Geographic/Getty Images)

That decline would be even faster if not for undersea jewels. Debmarine, De Beers’ exclusive joint venture with the Namibian government, says 60% of local Namibian diamonds currently come from the sea and predicts that could soon rise to 94%. Since undersea mining began 14 years ago, 16 million carats have been mined at sea and 62 million on land in Namibia.

Debmarine uses five vessels fitted with either drills or a giant “tractor” that sucks up sediment from the seabed. This is passed through filters and x-rays to separate out the gems. The tractor alone hoovers up 630 metric tons of material every hour yielding around 80 carats, which is a palmful of stones.

Plenty of other miners are following Debmarine’s example: Twenty-six seabed-mining licenses have since been granted to firms from various countries for sites in the Pacific’s international waters.

De Beers’ parent company, Anglo American, owns shares in Nautilus and will be watching these early explorations with interest. It might also soon have company on the Namibian seabed: In October 2016, the first phosphate-mining firm got government permission to start exploring the deep sea.

This piece is featured in Quartz’s new book The Objects that Power the Global Economy.

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