Published: Sat, March 10, 2018
Sci-tech | By Carrie Guzman

Diamond discovery under pressure

Diamond discovery under pressure

A schist in the hand may be quite continental, but diamonds are a geologist's best friend.

Trapped in the rigid structure of diamonds formed deep in the Earth's crust, scientists have discovered a form of water ice that was not previously known to occur naturally on our planet.

The mineral, called calcium silicate perovskite, is the fourth-most abundant mineral on Earth with zetta-tonnes (or 10²¹ tonnes) of it deep below Earth's surface.

"Usually the extremely deep minerals that come up to the surface are not stable once they experience low pressures", Rossman said.

"The only possible way of preserving this mineral at the Earth's surface is when it's trapped in an unyielding container like a diamond", he explained. In fact, the diamond can offer valuable information about the Earth's core: "Nobody has ever managed to keep this mineral stable at the Earth's surface ..."

It is said to be the world's richest source of rare blue diamonds and has produced over a quarter of the planet's diamonds with a value higher than 400 carats.

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The authors of the paper, who ran X-ray and spectroscopy tests to confirm their suspicions, believe the perovskite-containing diamond likely formed some 700 km deep in the Earth and must have sustained 24 billion pascals of pressure, equivalent to 240,000 atmospheres.

This diamond discovery, Pearson said, is "a nice illustration of how science works". "The specific composition of the perovskite inclusion in this particular diamond very clearly indicates the recycling of oceanic crust into Earth's lower mantle. It provides fundamental proof of what happens to the fate of oceanic plates as they descend into the depths of the Earth", Pearson said in the statement.

The chunk of calcium silicate perovskite within the gemstone was visible with the naked eye after the diamond was polished, the researchers wrote, but proper analysis and imaging required an worldwide effort. Its occurrence is expected to be mostly in the areas where the slabs of the oceanic crust have taken a dive into Earth's mantle near the tectonic boundaries.

The natural convection of the mantle will eventually transport a portion of these diamonds to the surface of the Earth.

Researchers from the University of Alberta have found a never-before-seen mineral inside a diamond from the depths of South Africa. The diamonds were found in mines in China, Zaire, South Africa, and Sierra Leone and were exposed to X-ray studies at the particle accelerator found at the Argonne National Lab, in IL, the USA.

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