Sourcing

Scientists Found This New Deep-Earth Mineral Trapped in a Diamond

SourcingNov 18, 2021

Scientists Found This New Deep-Earth Mineral Trapped in a Diamond

Davemaoite isn’t found in nature because it can’t survive outside the high-pressure environment of Earth’s mantle.

Geochemists at the University of Nevada, Las Vegas discovered a new mineral that was carried to Earth’s surface in this diamond. (Photo credit: Aaron Celestian, Los Angeles County Natural History Museum)
Las Vegas—Inclusions are important not only in the study of their host gemstones but also for other scientific disciplines, and one recent discovery shows how much scientists rely on these imperfections to further their understanding.

The University of Nevada, Las Vegas said in a statement that its geochemists recently discovered a mineral never observed in nature thanks to a diamond that carried it to the surface.

The mineral—a calcium silicate perovskite dubbed “davemaoite”—was found trapped in a diamond and traveled up to the Earth’s surface from at least 410 miles deep in the lower mantle, located between the planet’s core and crust.

The mineral was theorized to exist but hadn’t ever been observed before since many lower-mantle minerals can only exist in a high-pressure environment; they “fall apart” before reaching the surface, UNLV said.

The strength of its host diamond—a greenish, octahedral-shaped stone—allowed the davemaoite to survive and make it to the top, where UNLV’s geochemists could study it.

UNLV mineralogist Oliver Tschauner, who studies “super-deep diamonds” to see what they can teach us about the Earth’s interior and led the study published in Science this month, believes davemaoite formed between 410 and 560 miles below the Earth’s surface.

The recently discovered specimen appears as “infinitesimal small dark specks” in the diamond, where it was secure.

But, “When we broke open the diamond, the [mineral] stayed intact for about a second, then we saw it expand and bulge under the microscope and basically turn into glass,” Tschauner is quoted as saying in New Scientist.

 Related stories will be right here … 

The inclusions are only 5-10 micron in diameter, so Tschauner and his team analyzed its interior using X-ray fluorescence spectroscopy, X-ray diffraction, and infrared transmission spectrometry, finishing with laser-ablation ICP-mass spectrometry (LA-ICP-MS) for a full chemical analysis.

He said the material analyzed by LA-ICP-MS is gone, but added they scanned the sample by micro-X-ray diffraction afterward and found a weak signal of davemaoite, thereby noting there was still some material left inside.

The diamond was recovered from Botswana’s Orapa mine in the 1980s. The specimen was originally part of the California Institute of Technology mineral collection, which acquired it from a diamond dealer in 1987.   

Davemaoite is one of three main minerals in Earth’s lower mantle and makes up about 5-7 percent of the material there, Tschauner told Nature. Importantly, it can host three of the major elements that affect heat production in Earth’s lower mantle.

The International Mineralogical Association (IMA) has officially approved davemaoite as a new natural mineral. 

It was named in honor of Ho-Kwang “Dave” Mao, an experimental geophysicist who created many of the techniques still used by scientists like Tschauner and his colleagues today. 

The specimen studied by UNLV is now in the collection of the Los Angeles County Natural History Museum.
Brecken Branstratoris the senior editor, gemstones at National Jeweler, covering sourcing, pricing and other developments in the colored stone sector.

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