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.
(SOUNDBITE OF SONG, "I AM A ROCK")
PAUL SIMON: (Singing) I am a rock. I am an island.
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