Reports

Local Structure and Chemical Shifts for Six-Coordinated Silicon in High-Pressure Mantle Phases

Science  18 Jan 1991:
Vol. 251, Issue 4991, pp. 294-298
DOI: 10.1126/science.251.4991.294

Abstract

Most of the earth's mantle is made up of high-pressure silicate minerals that contain octahedrally coordinated silicon (SiVI), but many thermodynamically important details of cation site ordering remain unknown. Silicon-29 nuclear magnetic resonance (NMR) spectroscopy is potentially very useful for determining short-range structure. A systematic study of silicon-29 chemical shifts for SiVI has revealed empirical correlations between shift and structure that are useful in understanding several new calcium silicates. The observed ordering state of a number of high-pressure magnesium silicates is consistent with the results of previous x-ray diffraction studies

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