Crystal structure of hydrous wadsleyite with 2.8% H[subscript 2]O and compressibility to 60 GPa
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Hydrous wadsleyite ({beta}-Mg{sub 2}SiO{sub 4}) with 2.8 wt% water content has been synthesized at 15 GPa and 1250 C in a multi-anvil press. The unit-cell parameters are: a = 5.6686(8), b = 11.569(1), c = 8.2449(9) {angstrom}, {beta} = 90.14(1){sup o}, and V = 540.7(1) {angstrom}{sup 3}, and the space group is I2/m. The structure was refined in space groups Imma and I2/m. The room-pressure structure differs from that of anhydrous wadsleyite principally in the increased cation distances around O1, the non-silicate oxygen. The compression of a single crystal of this wadsleyite was measured up to 61.3(7) GPa at room temperature in a diamond anvil cell with neon as pressure medium by X-ray diffraction at Sector 13 at the Advanced Photon Source, Argonne National Laboratory. The experimental pressure range was far beyond the wadsleyite-ringwoodite phase-transition pressure at 525 km depth (17.5 GPa), while a third-order Birch-Murnaghan equation of state (EoS) [V{sub 0} = 542.7(8) {angstrom}{sup 3}, K{sub T0} = 137(5) GPa, K{prime} = 4.6(3)] still fits the data well. In comparison, the second-order fit gives V{sub 0} = 542.7(8) {angstrom}{sup 3}, K{sub T} = 147(2) GPa. The relation between isothermal bulk modulus of hydrous wadsleyite K{sub T0} and water content C{sub H{sub 2}O} is: K{sub T0} = 171(1)-12(1) C{sub H{sub 2}O} (up to 2.8 wt% water). The axial-compressibility {beta}{sub c} is larger than both {beta}{sub a} and {beta}{sub b}, consistent with previous studies and analogous to the largest coefficient of thermal expansion along the c-axis.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1002891
- Journal Information:
- Am. Mineral., Vol. 95, Issue (11-12) ; 11, 2010; ISSN 0003-004X
- Country of Publication:
- United States
- Language:
- ENGLISH
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