Physics and Chemistry of Minerals

, Volume 13, Issue 4, pp 215–220 | Cite as

High-Pressure crystal chemistry of spinel (MgAl2O4) and magnetite (Fe3O4): Comparisons with silicate spinels

  • Larry W. Finger
  • Robert M. Hazen
  • Anne M. Hofmeister
Article

Abstract

High-pressure crystal structures and compressibilities have been determined by x-ray methods for MgAl2O4 spinel and its isomorph magnetite, Fe3O4. The measured bulk moduli, K, of spinel and magnetite (assuming K′=4) are 1.94±0.06 and 1.86±0.05 Mbar, respectively, in accord with previous ultrasonic determinations. The oxygen u parameter, the only variable atomic position coordinate in the spinel structure (Fd3m, Z=8), decreases with pressure in MgAl2O4, thus indicating that the magnesium tetrahedron is more compressible than the aluminum octahedron. In magnetite the u parameter is unchanged, and both tetrahedron and octahedron display the 1.9 Mbar bulk modulus characteristic of the entire crystal. This behavior contrasts with that of nickel silicate spinel (γ-Ni2SiO4), in which the u parameter increases with pressure because the silicon tetrahedron is relatively incompressible compared to the nickel octahedron.

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Copyright information

© Springer-Verlag 1986

Authors and Affiliations

  • Larry W. Finger
    • 1
  • Robert M. Hazen
    • 1
  • Anne M. Hofmeister
    • 1
  1. 1.Geophysical LaboratoryCarnegie Institution of WashingtonWashington, DCUSA

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