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.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Finger LW, Hazen RM, Yagi T (1979) Crystal structures and electron densities of nickel and iron silicate spinels at elevated temperature or pressure. Am Mineral 64:1002–1009
Finger LW, King HE (1978) A revised method of operation of the single-crystal diamond cell and refinement of the structure of NaCl at 32 kbar. Am Mineral 63:337–342
Fleet ME (1981) The structure of magnetite. Acta Crystallogr B37:917–920
Hamilton WC (1974) Angle settings for four-circle diffractometers. In: International Tables for X-ray Crystallography, 4. Kynoch Press, Birmingham, England, pp 273–284
Harrison HR, Aragon R (1978) Skull melter growth of magnetite (Fe3O4). Mat Res Bull 13:1097–1104
Hazen RM (1986) High-pressure crystal chemistry of chrysoberyl, Al2BeO4: Insights on the origin of olivine elastic anisotropy. Phys Chem Mineral: in press
Hazen RM, Finger LW (1979) Bulk-modulus-volume relationship for cation-anion polyhedra. J Geophys Res 84:6723–6728
Hazen RM, Finger LW (1982) Comparative Crystal Chemistry. Wiley, New York
Hazen RM, Finger LW, Mariathasan JWE (1985) High-pressure crystal chemistry of scheelite-type tungstates and molybdates. J Phys Chem Solids 46:253–263
Hill RJ, Craig JR, Gibbs GV (1979) Systematics of the spinel structure type. Phys Chem Mineral 4:317–339
Ishii M, Hiraishi J, Yamanaka Y (1982) Structure and lattice vibrations of Mg-Al spinel solid solution. Phys Chem Mineral 8:64–68
King HE, Finger LW (1979) Diffracted beam crystal centering and its application to high-pressure crystallography. J Appl Crystallogr 12:374–378
Lehmann MS, Larsen MK (1974) A method for location of the peaks in step-scan-measured Bragg reflections. Acta Crystallogr A30:580–584
Mao KH, Takahashi T, Bassett WA, Kinsland GL, Merrill L (1974) Isothermal compression of magnetite to 320 kbar and pressure-induced phase transformation. J Geophys Res 79:1165–1170
Swanson DK, Weidner DJ, Prewitt CT, Kandelin JJ (1985) Single crystal compression of γ-Mg2SiO4 (abstract). Trans Am Geophys Union (EOS) 66:370
Ralph RL, Finger LW (1982) A computer program for refinement of crystal orientation matrix and lattice constants from diffractometer data with lattice symmetry constants. J Appl Crystallogr 15:537–539
Wang H, Simmons G (1972) Elasticity of some mantle crystal structures 1. Pleonaste and hercynite spinel. J Geophys Res 77:4379–4392
Yamanaka T, Takeuchi Y (1983) Order-disorder transition in MgAl2O4 spinel at high temperatures up to 1,700° C. Z Kristallogr 165:65–78
Yamanaka T, Takeuchi Y, Tokonami M (1984) Anharmonic thermal vibrations of atoms in MgAl2O4 spinel at temperatures up to 1,933 K. Acta Crystallogr B40:96–102
Zachariasen WH (1967) A general theory of x-ray diffraction in crystals. Acta Crystallogr 23:558–564
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Finger, L.W., Hazen, R.M. & Hofmeister, A.M. High-Pressure crystal chemistry of spinel (MgAl2O4) and magnetite (Fe3O4): Comparisons with silicate spinels. Phys Chem Minerals 13, 215–220 (1986). https://doi.org/10.1007/BF00308271
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00308271