What the world's biggest diamonds hint about the Earth's mantle - CSMonitor.com
Diamonds are formed deep below the Earth’s crust in the mantle and are brought to the surface during volcanic eruptions, bringing with them tiny flecks of metal and minerals trapped inside. While these “inclusions” are cut out to sell the jewels, they offer scientists a unique look at the composition of the Earth’s interior.
"You really couldn't ask for a better vessel to store something in," Evan Smith, a diamond geologist at the GIA and an author of the study, told NPR. "Diamond is the ultimate Tupperware."
The GIA procured eight fingernail-sized chunks of left-over diamond scraps, which the research team cut open and ground up to look at using microscopes, lasers, magnets, and electron beams.
They found that the inclusions contained a mixture of iron, nickel, carbon, and sulfur, encased in a thin layer of fluid methane and hydrogen. The metallic inclusions indicated that the diamonds were formed under extreme pressure, in oxygen-deprived patches of liquid metal.
Furthermore, some samples also contained mineral inclusions that suggested the large diamonds form at much greater depths than smaller ones – as deep as 200 to 500 miles below the surface, Dr. Smith told NPR, while smaller diamonds form at roughly 90 to 120 miles down.
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