Incorporation of Ferric Iron in CaSiO3 Perovskite at High Pressure

Zhongwu Wang1, 2 and T. Yagi1
1 Institute for Solid State Physics, The University of Tokyo, Roppongi, Tokyo 106, Japan
2 GEMOC, School of Earth Sciences, Macquarie University, Sydney 2109, Australia

Abstract: Synthetic andradite (Ca3Fe2Si3O12) has been compressed to loading pressures >21 GPa and heated to ∼1000°C by a YAG laser in a Diamond Anvil Cell (DAC). After quenching to room temperature, X-ray diffraction of the sample, still held at 21 GPa, showed that andradite had transformed to a cubic perovskite type polymorph with a = 3.460(4) Å. Upon decompression the perovskite phase transformed into an amorphous phase. The density of the perovskite polymorph (Ca3Fe2Si3O12) is ∼13.6% greater than that of isochemical andradite at 21 GPa. Ferric iron replaces Ca2+ and Si4+ in the perovskite structure (Fe3+ + Fe3+ = Si4+ + Ca2+), giving a formula unit: (Ca,Fe3+)(Si,Fe3+)O3. The new Fe3+-rich Ca-perovskite may provide new insight into the controls on the electrical conductivity of the lower mantle.

Keywords: andradite • high pressure • X-ray diffraction • perovskite • lower mantle

Mineralogical Magazine; October 1998 v. 62; no. 5; p. 719-723; DOI: 10.1180/002646198547963
© 1998, The Mineralogical Society
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