gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/002646198547963 Letters Incorporation of Ferric Iron in CaSiO3 Perovskite at High Pressure Wang Zhongwu 1 2 Yagi T. 1 Institute for Solid State Physics, The University of Tokyo, Roppongi, Tokyo 106, Japan GEMOC, School of Earth Sciences, Macquarie University, Sydney 2109, Australia 10 1998 62 5 719 723 29 4 1998 23 6 1998 Copyright © 1998, The Mineralogical Society 1998 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