Ordering of hydroxyl defects in hydrous wadsleyite (β-Mg2SiO4)
-
S.C. Kohn
,
R.A. Brooker
Abstract
Samples of wadsleyite (β-Mg2SiO4) containing a range of dissolved water concentrations up to 1.5 wt% were synthesized at 1300 °C and 15 GPa. The samples were studied using 1H MAS NMR and FTIR spectroscopy to determine the ordering of OH within the structure. As the 1H NMR chemical shift and O-H stretching frequency are both known to be correlated with the O-H···O distances in silicate and other materials, the spectroscopic data were compared with O···O distances calculated from the published crystal structure of hydrous wadsleyite.
Using this approach we show that the hydroxyl ions in wadsleyite containing 0.8-1.5 wt% H2O are highly disordered, occupying at least 14 of the 17 possible O-H···O environments, including some with strong hydrogen bonding. In contrast, for low water concentrations (<0.4 wt%) the hydroxyl ions are less disordered, with four environments being much more abundant than the others are. Three of these environments appear to involve protonation of O1, in agreement with most previous suggestions, and the fourth is probably O2-H···O2.
It is probable that the degree of disorder will increase with increasing temperature, so it should be taken into account when predicting phase equilibria involving hydrous wadsleyite and when extrapolating data on density and elastic properties from room temperature measurements.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Presidential Address. Scales of disequilibrium and rates of equilibration during metamorphism
- Characterization of coexisting NH4- and K-micas in very low-grade metapelites
- Effect of sonic and ultrasonic frequencies on the crystallization of basalt
- Sulfur saturation limits in silicate melts and their implications for core formation scenarios for terrestrial planets
- Molecular water in beryl, VIAl2 [Be3Si6O18]·nH2O, as a function of pressure and temperature: An experimental study
- Fluid-induced nucleation of (Y + REE)-phosphate minerals within apatite: Nature and experiment. Part I. Chlorapatite
- X-ray spectroscopic investigations of fluids in the hydrothermal diamond anvil cell: The hydration structure of aqueous La3+ up to 300 °C and 1600 bars
- Fibrous nanoinclusions in massive rose quartz: HRTEM and AEM investigations
- Polysomatism in högbomite: The crystal structures of 10T, 12H, 14T, and 24R polysomes
- Ordering of hydroxyl defects in hydrous wadsleyite (β-Mg2SiO4)
- The crystal structure and cation ordering of Phase-X-(K1–x–n)2(Mg1–n[Al,Cr]n)2Si2O7H2x: A potential K- and H-bearing phase in the mantle
- Feasibility of determining the quantitative OH content of garnets with Raman spectroscopy
- Raman spectroscopic study of garnet inclusions in diamonds from the mantle transition zone
- Raman spectroscopy of Fe2O3 to 62 GPa
- Study of the (010) olivine surface by Rutherford backscattering spectrometry in channeling geometry
- Equation of state of dense hydrous magnesium silicate phase A, Mg7Si2O8(OH)6
- Si-F bonding in aluminosilicate glasses: Inferences from ab initio NMR calculations
- Monoclinic nearly stoichiometric wüstite at low temperatures
- On the nature of tincalconite
- Letters. Chloride ion sites in silicate and aluminosilicate glasses: A preliminary study by 35Cl solid-state NMR
- Nuclear magnetic resonance and infrared spectroscopic study of excess-boron olenite from Koralpe, Styria, Austria
