Post-ilmenite phases of silicates and germanates |
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| Authors: | Lin-Gun Liu |
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| Institution: | Research School of Earth Sciences, Australian National University, Canberra, A.C.T. Australia |
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| Abstract: | MgSiO3, ZnSiO3, MgGeO3, MnGeO3, and ZnGeO3 are the only silicates and germanates known to crystallize in the ilmenite-like structure at high pressures and high temperatures. With the exception of the zinc compounds, the above-mentioned ilmenites have all been found to transform to the orthorhombic modification of the perovskite structure at higher pressures. The ilmenite phase of ZnSiO3, on the other hand, transforms to its component oxide mixture with the rocksalt and rutile structures, whereas ZnGeO3 (ilmenite) transforms first to an as yet undetermined orthorhombic phase and then to its component oxide mixture. The direct transformation from the ilmenite to perovskite structures observed in the metasilicates and metagermanates is consistent with all other reported high-pressure post-ilmenite phases (CdTiO3, CdSnO3, MnVO3, and (Fe,Mg)TiO3). The observation of the ilmenite-perovskite transformation in MgSiO3 and its solid solutions towards Al2O3 suggests that MgO (rocksalt) + SiO2 (rutile) + Al2O3 (corundum) is not a stable mineral assemblage for the earth's lower mantle. |
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