Scientists have finally confirmed the existence of calcium silicate perovskite from the Earth’s lower mantle. The sample comes from at least 660 kilometers (410 miles) below our feet, brought forth by being stuck in a diamond. The mineral has been named davemaoite, and the findings are reported in the journal Science.
Calcium silicate perovskite is expected to be the fourth most abundant mineral on Earth – yet has been beyond our direct reach. A previous possible discovery in 2018 (also in a diamond) did not exactly match up with the properties expected for the mineral.
The mineral can be created in the lab using a laser to simulate high pressures – but once the pressure is removed, its cubic form falls apart, so until now it has not been possible to find it in its naturally occurring form. However, this diamond preserved it.
“The discovery is the result of decades of efforts, and the development and use of microanalytical techniques for identifying structures and compositions of micron-scale inclusions in diamonds,” lead author Dr Oliver Tschauner, from the University of Nevada, Las Vegas, said in an audio briefing.
The new work finally delivered on the long-sought mineral, highlighting some of its most intriguing properties. In particular, the team shows the crucial role played by the incredible pressure at which it formed. The paper describes the ability to host a variety of elements and this is extremely important for the geology of our planet.
“Structural and chemical analysis of the mineral showed that it is able to host a wide variety of elements, not unlike fitting bulky objects into garbage can,” the team wrote in the paper. “Specifically, it has a large amount of trapped potassium.”
Previously, it had been shown experimentally that such material can be a "garbage can" for radioactive uranium and thorium. Together with potassium, they are three major heat-producing elements. This is evidence that the abundance of davemaoite and its precious storage contributes to the creation of heat through the deeper layer of the mantle.
This find gives hope that other minerals that only exist at high pressures might one day be found. Davemaoite is only the second high-pressure phase silicate mineral confirmed in nature. The only other known one is called bridgmanite, found inside a highly shocked meteorite.
The mineral is named after Dr Ho-Kwang (Dave) Mao, a Chinese-American experimental geophysicist who contributed to high-pressure research over the past five decades. The name davemaoite was approved as a new natural mineral by the Commission of New Minerals, Nomenclature, and Classification of the International Mineralogical Association.