Best diamonds born of deep-mantle metallic liquid

WASHINGTON, Dec. 15 (UPI) -- In an effort to understand magmatic behavior deep in Earth's mantle, scientists have helped explain how and why the biggest, best diamonds are born of deep-lying metallic liquid.

Diamonds are carved by jewelers to enhance their shine. The scraps are called offcuts. As part of a recent study, researchers examined the composition of offcuts from the biggest, most valuable diamonds.

Scientists discovered tiny metallic fragments trapped inside many of the offcuts -- mixtures of metallic iron and nickel organized alongside crystalized carbon, sulfur, methane and hydrogen. The discovery suggests the largest gem diamonds are pure carbon crystalized from liquid metal.

"The existence of this metal mixture has broad implications for our understanding of deep Earth processes," Evan Smith of the Gemological Institute of America said in a news release.

In addition to tiny metallic fragments, scientists also found and analyzed tiny pieces of silicate trapped in the offcuts. The silicate's composition suggests gem diamonds are formed more than 240 miles beneath Earth's surface.

The new research -- detailed in the journal Science -- suggests the deepest regions of the mantle are oxygen deprived, or reduced. The lack of oxygen explains the formation of iron-nickel liquid metal.

"The fact that reduced regions can be found in the Earth's mantle has been theoretically predicted, but never before confirmed with actual samples," said Steven Shirey, a researcher at the Carnegie Institution for Science.