A diamond forged deep within Earth's interior held an unexpected discovery locked inside: a mineral never before seen in nature and one that cannot normally exist on the planet's surface.
The mineral, trapped inside a diamond that was first unearthed in an African mine in the 1980s, is thought to play a role in how heat flows in Earth's mantle, the thick layer of mostly solid rock that lies between the planet's crust and outer core. In a study published Thursday in the journal Science, researchers at the University of Nevada, Las Vegas, said the finding could help scientists better understand the evolution of Earth's interior.
The mineral is mostly made of calcium silicate and appeared as nondescript dark blemishes in the diamond. But what looked like mere imperfections turned out to be a natural sample of a compound that typically can't hold its structure outside the high-pressure environment of Earth's lower mantle.
Oliver Tschauner, a mineralogist at the University of Nevada, Las Vegas, and the study’s lead researcher, said it's the first time a so-called lower mantle mineral has been observed intact in nature.
"I think we were very surprised," Tschauner said in a statement. "We didn’t expect this."
The researchers named the mineral "davemaoite," after the retired geophysicist Ho-kwang "Dave" Mao, who pioneered research on how materials behave under extreme pressures.
Tschauner said the davemaoite likely originated at a depth of between 410 and 560 miles in the planet's interior. Lower mantle minerals tend to fall apart before they reach Earth's surface, but Tschauner said the diamond's strength helped preserve the mineral.
The diamond was uncovered decades ago in the Orapa mine in Botswana. In 1987, it was sold to a mineralogist at the California Institute of Technology, but in recent years, Tschauner and his colleagues were able to study its interior structure.
The researchers said their discovery could help them create more accurate models of Earth's interior. Davemaoite can host radioactive elements such as uranium and thorium, which generate huge amounts of heat in Earth's lower mantle. Understanding how heat moves through the planet's interior could, in turn, shed light on how what happens in the mantle drives processes like plate tectonics, the scientists added.
The discovery also raises hope that other samples of lower mantle minerals could be found in nature, said Yingwei Fei, a geophysicist at the Carnegie Institution for Science, who was not involved with the study.
"Being able to obtain more direct samples from the inaccessible lower mantle would fill in our knowledge gap regarding the chemical composition and variability of our planet's depths," Fei said in a statement.
Tschauner said he hopes other minerals in larger quantities will be found in the future. Some, like davemaoite, could be lurking in unexpected places.
"For jewelers and buyers, the size, color, and clarity of a diamond all matter," he said, "and inclusions — those black specks that annoy the jeweler — for us, they're a gift."