Nature 262, 770 - 772 (26 August 1976); doi:10.1038/262770a0

The post-spinel phase of forsterite

LIN-GUN LIU

Research School of Earth Sciences, Australian National University, Canberra, ACT Australia

THE nature of the post-spinel phase of forsterite (the olivine structure of Mg₂SiO₄) and its importance to our understanding of the mineralogy, petrology and seismological discontinuities in the transition zone and the lower mantle of the Earth has attracted much recent attention^1,2. Kumazawa et al. ¹ reported that the post-spinel phase of forsterite recovered from 3.3 10¹⁰ Pa and 1,000 °C was a component oxide mixture of stishovite (SiO₂) plus periclase (MgO). In their studies of Mg₂SiO₄−Fe₂SiO₄ solid solutions at pressures up to 2.5 10¹⁰ Pa, Ming and Bassett² agreed with the conclusions of Kumazawa et al. Consequently, the oxide mixture seems to be widely accepted as the post-spinel phase of forsterite³. In this paper, however, I present results that disagree with this.

References

1.	Kumazawa, M., Sawamoto, H., Ohtani, E., and Masaki, K., Nature, 247, 356–358 (1974).
2.	Ming, L., and Bassett, W. A., Science, 187, 66–68 (1975).
3.	Hammond, A. L., Science, 190, 967–968 (1975).
4.	Liu, L., Geophys. Res. Lett., 2, 417–419 (1975).
5.	Liu, L., Nature, 258, 510–512 (1975).
6.	Liu, L., Earth planet. Sci. Lett., 31, 200–208 (1976).
7.	Ming, L., and Bassett, W. A., Earth planet. Sci. Lett., 27, 85–89 (1975).
8.	Liebertz, J., and Rooymans, C. J. W., Phys. Chem. Neue Folge, 44, 242–249 (1965).
9.	Syono, Y., Akimoto, S., and Endoh, Y., J. Phys. Chem. Solids, 32, 243–249 (1971).
10.	Liu, L., Phys. Earth planet. Int., 10, 167–176 (1975).
11.	Liu, L., Earth planet. Sci. Lett. (in the press).
12.	Ito, E., and Matsui, Y., Phys. Earth planet. Int., 9, 344–352, (1974).
13.	Liu, L., Earth planet. Sci. Lett., 24, 357–362 (1975).
14.	Ming, L., thesis, Univ. Rochester (1974).
15.	Ito, E., Matsui, Y., Suito, K., and Kawai, N., Phys. Earth planet. Int., 8, 342–344 (1974).
16.	Chao, E. C. T., Fahey, J. J., Littler, J., and Milton, D. J., J. geophys. Res., 67, 419–421 (1962).