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Magnesium coordination environments in glasses and minerals: New insight from high-field magnesium-25 MAS NMR

Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, U.S.A.

Correspondence: ^* E-mail: kroeker{at}pangea.stanford.edu

A comparison of ²⁵Mg magic angle spinning (MAS) NMR spectra of crystalline and glassy diopside (CaMgSi₂O₆) reveals that the chemical shift in the disordered phase corresponds to that of the mineral, suggesting that sixfold coordination is essentially retained upon vitrification. Likewise, a crystalline leucite analogue (K₂MgSi₅O₁₂) known to possess fourfold-coordinated Mg has the same peak position as the corresponding glass. In addition to being a sensitive probe of local structure by analogy with crystalline phases, these data may be understood in terms of the effect of competing cation field strengths: competing network modifier cations with higher field strength induce higher magnesium coordination numbers, with a consequent increase in bond length and decrease in chemical shift. This work demonstrates the utility of NMR at 14.1 Tesla for probing the coordination environment of Mg in glasses and minerals, and suggests great potential for high-field NMR investigations of quadrupolar nuclides with low resonance frequencies in amorphous systems.

This article has been cited by other articles:

				K. Shimoda, Y. Tobu, M. Hatakeyama, T. Nemoto, and K. Saito Structural investigation of Mg local environments in silicate glasses by ultra-high field 25Mg 3QMAS NMR spectroscopy American Mineralogist, April 1, 2007; 92(4): 695 - 698. [Abstract] [Full Text] [PDF]

				J. R. Allwardt, J. R. Allwardt, and J. F. Stebbins Ca-Mg and K-Mg mixing around non-bridging O atoms in silicate glasses: An investigation using 17O MAS and 3QMAS NMR American Mineralogist, May 1, 2004; 89(5-6): 777 - 784. [Abstract] [Full Text] [PDF]