Davemaoite, the first calcium silicate perovskite from Earth’s lower mantle, discovered inside deep-earth diamond

For the first time, a high-pressure calcium silicate perovskite (CaSiO₃) has been identified as a naturally occurring mineral from Earth’s lower mantle, researchers report. The newly discovered crystalline compound, named davemaoite by the authors, was found trapped as an inclusion inside a deep-earth diamond, which formed at high-pressure and temperature more than 660 kilometers below the Earth’s surface. Davemaoite was named in honor of Ho-kwang (Dave) Mao – a prominent experimental high-pressure geophysicist – and confirmed as a new mineral by the International Mineralogical Association. According to Oliver Tschauner and colleagues, calcium silicate perovskite (CaSiO₃) is among the most geochemically important minerals in the lower mantle, largely because it concentrates elements that are incompatible in the upper mantle, including rare-earth elements and radioactive isotopes that make an important contribution to the heat of Earth’s mantle. Although theorized for decades, to date, no one has ever successfully retrieved a high-pressure phase silicate from the Earth’s lower mantle, largely because they cannot retain their mineralogical structure after being removed from a high-pressure, high-temperature environment. The only other high-pressure phase silicate mineral confirmed in nature, bridgmanite, was found inside a highly shocked meteorite. In this study, Tshauner et al. identified and characterized the davemaoite inclusion within the deep-earth diamond using synchrotron x-ray diffraction. They show its ability to host a wide variety of elements in its structure, including potassium, thorium and uranium – three of the major heat-producing elements. The findings support the existence of compositional heterogeneity within the lower mantle and, given the mineral’s overall abundance, suggest that davemaoite likely influences heat generation in the deep mantle. “The work by Tschauner et al. inspires hope in the discovery of other difficult high-pressure phases in nature, either through careful search in deep-origin diamonds or in highly shocked meteorites,” writes Yingwei Fei in a related Perspective. “Such direct sampling of the inaccessible lower mantle would fill our knowledge gap in chemical composition and heterogeneity of the entire mantle of our planet.”

For reporters interested in trends, several past Science publications featuring the work of Oliver Tschauner and others have presented findings related to lower mantle minerals, including a November 2014 report that described the discovery of “bridgemanite” in a shocked meteorite – the only other high-pressure mineral confirmed in nature.

Also, a March 2018 report by Tschauner et al. used deep-earth diamonds to discover inclusions of ice-VII – a cubic crystalline form of ice that forms when aqueous water is trapped and subjected to extremely high pressure.