Rare Deep Diamond With Perovskite Shows Ocean Crust Recycles Into Earth's Mantle

Henrietta Brewer
March 11, 2018

Probably not a huge discovery, you may think, but this ice, names Ice-VII, is coming from the Earth's mantle and has been supposed, until now, that it only naturally exists on other planets and their moons and can only be made in a lab. "The only possible way of preserving this mineral at Earth's surface is when it's trapped in an unyielding container like a diamond". Despite this relatively shallow depth, the researchers determined that the crystal was an example of a "deep diamond" that most likely had been formed about 700 km below the Earth's surface, derived from a subducted slab of ocean crust and exposed to some 240,000 atmospheres of pressure.

The diamond was found in Cullinan Mine, a mine from South Africa.

The paper on the perovskite diamond appeared online Wednesday in the journal Nature, under the title "CaSiO3 perovskite in diamond indicates the recycling of oceanic crust into the lower mantle".

"Laboratory experiments and seismology data have created a clear theoretical picture of the most abundant minerals that comprise the deeper parts of the Earth's mantle".

"Nobody has ever managed to keep this mineral stable at the Earth's surface", study co-author Graham Pearson, a professor in the University of Alberta's Department of Earth and Atmospheric Sciences, said in a statement. The recent find also yielded interesting information about the processes that shape Earth, offering strong evidence of a very deep "recycling" of oceanic crusts, as the authors of the study put it.

Cullinan Mine is known as the source of some of the world's largest diamonds. Surprisingly, Silicate perovskite is actually considered to be our planet's fourth most abundant mineral.

Pearson gave an estimate of around 24 billion pascals which is the pressure sustained by such kind of diamond. While most diamonds are formed at a depth of about 150 to 200 km, this one possibly formed at a depth of at least 700 km, notes the report. According to Pearson, diamonds are naturally formed stones which are both commercially valuable and have a great scientific value as it provides insights about the depth of Earth's core and the details regarding how it formed, etc.

The researchers polished the diamond and conducted spectroscopic analysis to confirm that the mineral inside it is indeed the perovskite.

"The diamond lattice doesn't relax much, so the volume of the inclusion remains nearly constant whether it's in the Earth's mantle or in your hand", said Oliver Tschauner, a professor of geoscience at the University of Nevada, Las Vegas. "It provides fundamental proof of what happens to the fate of oceanic plates as they descend into the depths of the Earth", he added.

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