Megadiamonds point to metal in mantle | Science News

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Megadiamonds point to metal in mantle

Glimpse of deep Earth chemistry found in rare gems’ imperfections

By
2:07pm, December 15, 2016
diamond

DEEP DIVE Metal shards (black spots) in this diamond hold clues to the deep-Earth environment in which it formed.

Imperfections in supersized diamonds are a bummer for gem cutters but a boon for geologists. Tiny metal shards embedded inside Earth’s biggest diamonds provide direct evidence that the planet’s rocky mantle contains metallic iron and nickel, scientists report in the Dec. 16 Science.

The presence of metal in the mantle is “something that’s been predicted in theory and experiments for a number of years, but this is the first time that we have samples that give us physical evidence,” says Evan Smith, a geologist at the Gemological Institute of America in New York City who led the study.

Understanding the composition of the mantle can help scientists figure out how it drives plate tectonics, and how elements like carbon and oxygen are cycled and stored in the Earth.

Diamonds form in the mantle when carbon-containing compounds are compressed and heated to

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