Physics and Chemistry of Minerals

, Volume 14, Issue 1, pp 13–20 | Cite as

High-pressure crystal chemistry of chrysoberyl, Al2BeO4: Insights on the origin of olivine elastic anisotropy

  • Robert M. Hazen
Article

Abstract

High-pressure crystal structure refinements and axial compressibilities have been determined by x-ray methods for the olivine isomorph chrysoberyl, Al2BeO4. Unlike silicate olivines, which are more than twice as compressible along b than along a, chrysoberyl (space group Pbnm) has nearly isotropic compressibility with βa=1.12±0.04, βb=1.46±0.05, and βc=1.31±0.03 (all×10−4 kbar−1). The resultant bulk modulus is 2.42±0.05 Mbar, with K′ assumed to be 4. The axial compression ratios of chrysoberyl are 1.00:1.30:1.17, compared to axial compression ratios 1.00:2.02:1.60 for forsterite. These differences in compression anisotropy arise from differences in relative bond compressibilities. In chrysoberyl the average aluminum-oxygen and beryllium-oxygen bond compressibilities are similar, yielding nearly isotropic compression, but in silicate olivines octahedral cation-oxygen bonds are significantly more compressible than Si-O bonds, so that compression parallel to a is much more restricted than that parallel to b. The inherent anisotropy of the olivine structure is not, by itself, sufficient to cause anisotropic compression. It appears that in the case of olivine the distribution of cations of different valences, in conjunction with the structure type, leads to anisotropies in physical properties.

Key words

Chrysoberyl compressibility high-pressure structure equation-of-state elasticity 

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References

  1. Au AY, Hazen RM (1985) Polyhedral modeling of the elastic properties of corundum (α-Al2O3) and chrysoberyl (Al2BeO4). Geophys Res Lett 12:725–728Google Scholar
  2. Barton MD (1986) Phase equilibria and thermodynamic properties of minerals in the BeO-Al2O3-SiO2-H2O (BASH) system, with petrologic applications. Am Mineral 71:277–300Google Scholar
  3. Bragg WL, Brown GB (1926) Die Struktur des Olivins. Z Kristallogr 63:538Google Scholar
  4. Farrell EF, Fang JH, Newnham RE (1963) Refinement of the chrysoberyl structure. Am Mineral 48:804–810Google Scholar
  5. 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 63:337–342Google Scholar
  6. Graham EK, Barsch GR (1969) Elastic constants of single-crystal forsterite as a function of temperature and pressure. J Geophys Res 74:5949–5960.Google Scholar
  7. Hamilton WC (1974) Angle settings for four-circle diffractometers. In: International Tables for X-ray Crystallography, 4:273–284. Kynoch Press, Birmingham, EnglandGoogle Scholar
  8. Hazen RM (1977) Effects of temperature and pressure on the crystal structure of ferromagnesian olivine. Am Mineral 62:309–315Google Scholar
  9. Hazen RM, Finger LW (1979) Bulk-modulus-volume relationship for cation-anion polyhedra, J Geophys Res 84:6723–6728Google Scholar
  10. Hazen RM, Finger LW (1980) Crystal structure of forsterite at 40 kbar. Carnegie Inst Washington Yearbook 79:364–367Google Scholar
  11. Hazen RM, Finger LW (1982) Comparative crystal chemistry. Wiley, New YorkGoogle Scholar
  12. Hazen RM, Finger LW, Mariathasan JWE (1985) High-pressure crystal chemistry of scheelite-type tungstates and molybdates. J Phys Chem Solids 46:253–263Google Scholar
  13. King HE, Finger LW (1979) Diffracted beam crystal centering and its application to high-pressure crystallography. J Appl Crystallogr 12:374–378Google Scholar
  14. Kudoh Y, Takeuchi Y (1985) The crystal structure of forsterite Mg2SiO4 under high pressures up to 149 kbar. Z Kristallogr 171:291–302Google Scholar
  15. Kudoh Y, Takeda H (1986) Single crystal x-ray diffraction study on bond compressibility of fayalite, Fe2SiO4 and rutile, TiO2 under high pressure. Proc 10th AIRAPT Conf, in pressGoogle Scholar
  16. Kumazawa M, Anderson OL (1969) Elastic moduli, pressure derivatives, and temperature derivatives of single-crystal olivine and single-crystal forsterite. J Geophys Res 74:5961–5972Google Scholar
  17. Lehmann MS, Larsen FK (1974) A method for location of the peaks in step-scan-measured Bragg reflections. Acta Crystallogr A30:580–584Google Scholar
  18. Liebermann RC (1982) Elasticity of minerals at high temperature and pressure. In: Schreyer W (ed.) High-Pressure Research in Geoscience. E. Schweizerbart'sche Verlagsbuchhandlung, StuttgartGoogle Scholar
  19. 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 15:537–539Google Scholar
  20. Sharp ZD, Hazen RM, Finger LW (1986) Structural refinements of monticellite to 60 kbar. GSA Abstracts with Program, in pressGoogle Scholar
  21. Shimizu H, Bassett WA, Brody EM (1982) Brillouin-scattering measurements of single-crystal forsterite to 40 kbar at room temperature. J Appl Phys 53:620–626Google Scholar
  22. Sumino Y, Nishizawa O, Goto T, Ohno I, Ozima M (1977) Temperature variation of elastic constants of single-crystal forsterite between-190° and 400° C. J Phys Earth 25:377–392Google Scholar
  23. Suzuki I, Anderson OL, Sumino Y (1983) Elastic properties of a single-crystal forsterite Mg2SiO4, up to 1,200 K. Phys Chem Minerals 10:38–46Google Scholar
  24. Swanson DK, Weidner DJ, Prewitt CT, Kandelin JJ (1985) Single-crystal compression of γ-Mg2SiO4 (abstract). Trans Am Geophys Union (EOS) 66:370Google Scholar
  25. Wang H, Gupta MC, Simmons G (1975) Chrysoberyl (Al2BeO4): Anomaly in velocity-density systematics. J Geophys Res 80:3761–3764Google Scholar
  26. Zachariasen WH (1967) A general theory of x-ray diffraction in crystals. Acta Crystallogr 23:558–564Google Scholar

Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • Robert M. Hazen
    • 1
  1. 1.Geophysical LaboratoryCarnegie Institution of WashingtonWashington, DCUSA

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