Small black specks in a diamond from an African mine have turned out to be a vital ingredient of the deep Earth, identified in nature for the first time after decades of searching.

It is a rare glimpse of a mineral that normally cannot exist on Earth’s surface but plays a major part in heat flow deep inside the planet, says Oliver Tschauner, a geochemist at the University of Nevada, Las Vegas. He led the team that reported the discovery on 11 November in Science1.

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