Phase relations of bridgmanite, the most abundant mineral in the Earth's lower mantle

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Katsura, Tomoo:
Phase relations of bridgmanite, the most abundant mineral in the Earth's lower mantle.
In: Communications Chemistry. Bd. 8 (2025) . - 28.
ISSN 2399-3669
DOI: https://doi.org/10.1038/s42004-024-01389-8

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Abstract

The knowledge of phase relations of constitutive minerals is essential to investigate the structure, dynamics and evolution of the Earth and planetary interiors. This paper reviews the phase relations of bridgmanite, the most abundant mineral in the Earth’s lower mantle, with an ideal composition of MgSiO3. Bridgmanite has an orthorhombic structure with larger dodecahedral A and smaller octahedral B cation sites. The A-sites can incorporate Mg2+, Fe2+, Fe3+, and Al3+, while the B-sites accommodate Si4+, Al3+ and Fe3+. The incorporation of hydrogen and large cations like Ca is likely limited, although these issues are still debated. Al3+ and Fe3+, respectively, can form the charge-coupled components, AlAlO3 and Fe3+Fe3+O3 occupying both A- and B-sites. When both Al3+ and Fe3+ are present, Al3+ occupies B-sites, and Fe3+ occupies A-sites, forming Fe3+AlO3. In systems with excess MgO, Al and Fe3+ also form the oxygen vacancy components MgAl3+O2.5□0.5 and MgFe3+O2.5□0.5. The phase relationships of bridgmanite with coexisting phases are discussed as a function of pressure, temperature, and oxygen fugacity from the simple MgSiO3 system to the complex MgO-Fe2+O-Fe3+2O3-Al2O3-SiO2 system.