The mineral Davemaoite (CaSiO3-perovskite, the third most abundant mineral in lower mantle layer of Earth’s interior) has been discovered on the surface of the Earth for the first time. It was found trapped inside a diamond. Perovskite is found naturally ONLY in lower mantle layer of the interior of the Earth under extremely high temperature and pressure conditions. This first-ever discovery of interior earth mineral in nature is important to geology for better understanding of dynamics of deep Earth.
Perovskite is a mineral consisting of calcium titanium oxide (CaTiO3). Any other mineral having similar crystal structure is called a perovskite. This makes perovskite a class of compounds which have the same type of crystal structure as CaTiO3 (perovskite structure).
Calcium-silicate perovskite (CaSiO3-perovskite or CaPv) is an important mineral because it is the third most abundant mineral1 (7% by volume) in the lower mantle layer of Earth’s interior and plays a significant role in the heat dynamics of Earth’s interior. To put things in perspective, of the three layers of Earth, the mantle layer, between dense super-heated core and thin outer crust layer, makes up 84% of Earth’s total volume while the lower mantle layer alone comprises 55 percent of the Earth and extends from 670 and 2900 km in depth. The below table gives a snapshot view of place of perovskite in Earth’s interior.
Table: Place of perovskite rich layer in Earth’s interior
|Depth (from surface to core)||Earth’s layer ||Temperature ||Composition and state |
|100-670 km||Outer mantle (Upper mantle)||200 °C to 900 °C ||almost exclusively solid, can only flow very slowly, made of rocks, about 55% olivine and 35% pyroxene, and 5 to 10% of calcium oxide and aluminum oxide. |
|670 –2900 km||Inner mantle (Lower mantle) ||1650 °C to 2350 °C ||mainly composed of three minerals – bridgmanite, ferropericlase, and calcium-silicate perovskite (CaSiO3-perovskite). Rocks of the mantle have plasticity so they creep in response to temperature and pressure. Mantle convection is the phenomenon of upward movement of mantle material transferring heat from the core towards surface.|
|2900 – 5100 km||Outer core ||2204 °C to 4982 °C||made of liquid metals |
|5100 – 6378 km||Inner core ||4,982° C ||made of solid metals |
Perovskites along with other minerals in the mantle layer play a key role in the dynamics of deep earth involving heat transfer from core towards surface, called mantle convection. Despite its abundance and importance, perovskite has never been retrieved from the lower mantle layer, because it loses its structure on being removed from its high-pressure conditions.
Researchers have now reported discovery of calcium silicate perovskite as a diamond inclusion in a natural sample. The diamond was found in Orapa mine, Botswana decades ago and was purchased by a mineralogist of USA in 1987. The team of researchers had been studying the diamond for few years for any entrapped deep-Earth mineral.
The research team led by Oliver Tschauner employed synchrotron x-ray diffraction to study the internal structure of the infinitesimally small dark specks in a diamond thought to be perovskite from the lower mantle layer and were able to find definitive evidence of structurally preserved cubic CaSiO3-perovskite there2.
Further structural and chemical studies indicated that the mineral had large amounts of trapped potassium implying that this perovskite could host three of the major heat-producing elements (uranium and thorium were previously known) which influence heat generation in Earth’s interior. They named the mineral “davemaoite” (after geophysicist Ho-kwang “Dave” Mao) which was approved as a new natural mineral. The researchers think that the mineral may have originated from lower mantle layer between 650 and 900 km deep below the Earth’s surface 3,4.
Surprisingly, CaSiO3 perovskite was reported to be discovered in a deep-Earth diamond from South Africa in 2018 however the research team had not claimed official discovery of a new mineral 5.
This discovery, in conjunction with further discoveries of more minerals in future, should enrich the understanding of evolution of Earth’s mantle.
- Zhang Z., et al 2021. Thermal conductivity of CaSiO3 perovskite at lower mantle conditions. Physical Review B. Volume 104, Issue 18 – 1. Published 4 November 2021. DOI: https://doi.org/10.1103/PhysRevB.104.184101
- Fei,Y. 2021. Perovskite retrieved from the lower mantle, Science. Published 11 Nov 2021. Vol 374, Issue 6569 pp. 820-821. Science (2021). DOI: https://doi.org/10.1126/science.abm4742
- Tschauner, O. et al. Discovery of davemaoite, CaSiO3-perovskite, as a mineral from the lower mantle. Science. 11 Nov 2021. Vol 374, Issue 6569 pp. 891-894. DOI: https://doi.org/10.1126/science.abl8568
- University of Nevada 2021. News – Research in Brief: First-Ever Interior Earth Mineral Discovered in Nature. [Posted 15 November 2021. Available online at https://www.unlv.edu/news/release/research-brief-first-ever-interior-earth-mineral-discovered-nature
- Nestola, F., Korolev, N., Kopylova, M. et al. CaSiO3 perovskite in diamond indicates the recycling of oceanic crust into the lower mantle. Nature 555, 237–241 (2018). https://doi.org/10.1038/nature25972