Never-Before-Seen Mineral Found Inside a Diamond

The diamond acted as a container, keeping a piece of calcium silicate perovskite stable as it moved towards the Earth’s surface

Nester Korolev/University of British Columbia

Calcium silicate perovskite (CaSiO3) is thought to be the fourth most abundant mineral on the planet, but until recently, it had never been observed in nature. Above about 400 miles beneath the Earth’s surface, this elusive mineral becomes unstable. But as Michelle Starr of Science Alert reports, researchers have found a piece of CaSiO3 that managed to make it close to the surface of the Earth, encased in a tiny diamond.

The diamond sliver was discovered at South Africa's Cullinan diamond mine, which is best known for yielding two of the largest diamonds in the British Crown Jewels. According to Brandon Specktor of Live Science, the piece of CaSiO3 was visible to the naked eye once the diamond was polished, but an international team of researchers collaborated on analyzing the precious stone with X-ray and spectroscopy tests. They published the results of this analysis in the journal Nature.

The diamond was discovered less than 0.6 miles below the Earth’s surface, but the researchers note in the study that it was in fact a “super-deep” diamond. Most of these sparkly stones originate between 93 and 124 miles below the Earth’s surface. The one containing the CaSiO3 likely formed at a depth of around 435 miles, where the pressure is approximately 240,000 times greater than the atmospheric pressure at sea level. When this extreme force formed the diamond, the CaSiO3 was trapped inside.

The mineral did not deform as the diamond moved towards the Earth’s surface because the diamond acted as “an unyielding container,” Graham Pearson, a mantle geochemist at the University of Alberta and a co-author of the study, explains in a statement.

Pearson also says that the findings of the new analysis suggest there may be “as much as zetta tonnes of this perovskite in deep Earth.” (Zetta is a unit prefix equal to a factor of 1021, or a one followed by 21 zeros.) Scientists have long known that CaSiO3 was plentiful, particularly in “slabs of oceanic crust that have plunged into the planet's mantle at tectonic boundaries,” Specktor of Live Science writes. But since nobody has been able to keep the mineral stable at accessible depths, it has proven very difficult to study.

Researchers at the University of British Columbia are now working to learn more about the mineral’s age and origin. 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. 

“[T]he specific composition of the perovskite inclusion in this particular diamond very clearly indicates the recycling of oceanic crust into Earth's lower mantle,” Pearson said in the statement. “It provides fundamental proof of what happens to the fate of oceanic plates as they descend into the depths of the Earth.”

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