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Earth’s rarest diamonds form from primordial carbon in the mantle

The planet’s carbon cycle may not go as deep as scientists have thought

Hope Diamond

Superdeep diamonds, such as the Hope Diamond, are formed in an ancient reservoir of carbon in the lower mantle that is separate from the carbon cycle that operates at Earth’s surface.

Smithsonian National Museum of Natural History

By Carolyn Gramling

- More than 2 years ago

Most diamonds are made of carbon recycled over and over again between Earth’s surface and its crust.