High-pressure elasticity of a natural magnetite crystal

Hans J. Reichmann*, Steven D. Jacobsen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

64 Scopus citations

Abstract

Variation of the sound velocities, elastic constants, and compressibility of a natural magnetite crystal were determined using gigahertz ultrasonic interferometry and single-crystal X-ray diffraction to 8.7 GPa. At ambient pressure, the elastic constants are (in GPa): c 11 = 260.5(1.0), c 12 = 148.3(3.0), and c 44 = 63.3(1.5). While c 11 and c 12 have similar positive pressure derivatives of 5.14(13) and 5.39(10), respectively, the c 44 elastic constant exhibits mode-softening over this pressure range, with dc 44 /dP = -0.13(4), calculated from the pressure dependence of the [100] shear velocity. The adiabatic bulk modulus (K os ) is 185.7(3.0) GPa, with K s = 5.1(1), and the shear modulus (G o ) is 60.3(3.0) GPa, with G' = -0.1(1). The bulk modulus and its pressure derivative obtained dynamically are consistent with the isothermal equation of state, measured on the same sample by single-crystal X-ray diffraction, yielding K OT = 180.0(1.0) and K' T = 5.2(4). Pressure-induced shear-mode softening in magnetite is most likely related to magnetoelastic coupling and the first-order phase transition to an orthorhombic structure above 21 GPa.

Original languageEnglish (US)
Pages (from-to)1061-1066
Number of pages6
JournalAmerican Mineralogist
Volume89
Issue number7
DOIs
StatePublished - Jan 1 2004

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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