New mineral 'davemaoite' made an unlikely journey from the depths of the Earth

Nov 17, 2021
Originally published on November 17, 2021 3:53 pm

Researchers say they've recovered a mineral from deep inside the Earth — one they thought would never see the light of day.

Scientists at the University of Nevada, Las Vegas, named the mineral "davemaoite," after Ho-kwang "Dave" Mao, a retired experimental geophysicist whose influence on the field is still felt today.

"It's an opportunity to give him credit for his big contributions," said Oliver Tschauner, a mineralogist who led a study of the rare mineral, in an interview with NPR's Morning Edition.

No one ever expected to see the mineral on the Earth's surface.

That's because deep-Earth minerals like davemaoite aren't suited to survive outside the high-pressure environments where they're made. But this sample of davemaoite did survive. Trapped inside a diamond, the mineral made the more than 410-mile journey to the Earth's surface from its lower mantle — the layer between the planet's core and crust. Without the diamond's strength, the davemaoite would've fallen apart.

"That was, a little bit of luck that we found it," said Tschauner.

Scientists in 1975 had previously theorized that the crystalized compound, calcium silicate perovskite, existed within the Earth's mantle. But now they have proof, marking "the first time that lower mantle minerals have ever been observed in nature," according to a news release from the university on Monday.

The diamond-encased mineral was mined in Botswana before a gem dealer sold it to a mineralogist at the California Institute of Technology in Pasadena.

The mineral was spotted among tiny inclusions — or specks — within the diamond.

"Jewelers, of course, want the flawless diamond — the one that does not have any inclusions," said Tschauner.

When Tschauner and his team finally got hold of the rarity, they used what he described as a specialized X-ray, known as a synchrotron, to study it.

The finding will help scientists get a clearer picture of the evolution of the Earth's mantle, according to Tschauner. Scientists also believe davemaoite plays a key role in generating heat flow in the Earth's mantle, which in turn drives processes such as plate tectonics that reshape the Earth's landmasses.

And it's official: Last year, before Tschauner's team published their findings, the International Mineralogical Association added davemaoite to its list of minerals. As for the sample itself, it's now in safe-keeping at the Los Angeles Natural History Museum.

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NOEL KING, HOST:

All right, there's one less mystery underground thanks to Dr. Oliver Tschauner and his team of geophysicists.

OLIVER TSCHAUNER: That was a little bit of luck that we found it.

A MARTINEZ, HOST:

Their discovery - a mineral called davemaoite, which they named after a fellow scientist.

TSCHAUNER: Dave Mao - Ho-Kwang Mao - is a experimental geophysicist who has developed much of the techniques that they're using. So I thought it's a opportunity to give him credit for his big contributions.

MARTINEZ: He, along with other scientists, developed a theory that this mineral existed deep down inside the Earth's mantle. But it's very rare to find it near the surface.

KING: Yeah, because it requires a precise combination of heat and pressure to form. And you only find that combo hundreds of miles beneath us.

TSCHAUNER: We did not expect that this mineral can be recovered or found ever in a terrestrial environment.

KING: But a twist - then they did find it in a diamond from Botswana.

MARTINEZ: That rock wasn't very popular with jewelers.

TSCHAUNER: Jewelers, of course, want a flawless diamond - the one that does not have any inclusions. And the diamonds we are looking at are those that contain inclusions.

MARTINEZ: Inclusion is another word for speck. And the speck they found was tiny - only a few micrometers. So they needed a kind of super X-ray called a synchrotron to study it.

TSCHAUNER: You have to go to this large facility. It's nothing that you can build on a campus or in your own lab.

KING: Dr. Tschauner says this discovery is hard proof of geothermal processes going on deep beneath the surface of the Earth.

TSCHAUNER: So real samples from a known depth in the Earth mantle with a known composition that we can use to understand those processes.

KING: And the diamond itself is safely locked away at the Los Angeles Natural History Museum, where geophysicists can access it.

MARTINEZ: And if you're the Dave Mao, go break yourself off a piece of that rock. It's got your name on it.

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