Abstract
THE polymorphic transformation of (Mg,Fe)2SiO4 from the olivine structure type (denoted I) to the spinel type (denoted III) plays a key part in the Earth's mantle at depths between 350 and 1,000 km. The situation is complicated, for Ringwood and Major1 synthesized yet a third phase for compositions more magnesian than Mg0.85Fe0.15, which overlap the range Mg0.8 to Mg0.9 thought to represent mantle material. This phase (denoted II) possesses an X-ray powder diffraction pattern the strong lines of which are similar to those of spinel, but which contains many extra weak lines. It is optically birefringent. Ringwood and Major suggested that the phase may be a distorted spinel, and that the distortion occurred during quenching of an original true spinel.
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References
Ringwood, A. E., and Major, A., Earth Planet. Sci. Lett., 1, 241 (1966).
Akimoto, S., and Sato, Y., Tech. Rep. Inst. Solid State Physics, The University of Tokyo, Ser. A, No. 328 (1968).
Ringwood, A. E., and Major, A., Earth Planet. Sci. Lett., 1, 351 (1966).
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MOORE, P., SMITH, J. High Pressure Modification of Mg2SiO4: Crystal Structure and Crystallochemical and Geophysical Implications. Nature 221, 653–655 (1969). https://doi.org/10.1038/221653a0
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DOI: https://doi.org/10.1038/221653a0
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