Investigation of Al,Si Order in K-feldspars Using 27Al and 29Si MAS NMR

Yuehui Xiao, R. James Kirkpatrick, Richard L. Hay, Youn Joong Kim and Brian L. Phillips
Dept. of Geology, University of Illinois, Urbana, IL 61801, USA
Division of Materials Science and Engineering, University of California, Davis, CA 95616, USA

Abstract: This paper presents a 27Al and 29Si MAS NMR study of K-feldspars and demonstrates that the spectra are sensitive to variations in the state of Al,Si order. For synthetically annealed samples, the results are in agreement with previous IR spectroscopy (Harris et al., 1989) and demonstrate that Al,Si rearrangement continues after the samples have become monoclinic as determined by powder XRD. NMR methods provide a significantly improved picture of the state of local Al,Si order in such samples. For triclinic samples, measures of the state of Al,Si order (M1 and M2 of 27Al spectra and M2 of 29Si spectra) correlate well with site occupancies determined by powder XRD, but for the monoclinic samples the NMR parameters continue to change whereas the XRD parameters do not. Interpretations based on the NMR results for the synthetically disordered samples are consistent with 1-step disordering, as observed by XRD. 27Al and 29Si MAS NMR is likely to be a useful tool for probing the state of local Al,Si order in a wide variety of natural samples.

Keywords: Al,Si order • K-feldspars • nuclear magnetic resonance

Mineralogical Magazine; March 1995 v. 59; no. 394; p. 47-61; DOI: 10.1180/minmag.1995.59.394.05
© 1995, The Mineralogical Society
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