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(super 23) Na, (super 29) Si, and (super 71) Ga MAS-NMR spectroscopy of synthetic gallian- fluor-amphiboles

Barbara L. Sherriff, David M. Jenkins, Gerald Kunath-Fandrei, Steffen Goetz and Christian Jaeger
(super 23) Na, (super 29) Si, and (super 71) Ga MAS-NMR spectroscopy of synthetic gallian- fluor-amphiboles
American Mineralogist (August 1999) 84 (7-8): 1033-1040

Abstract

A magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopic study was done on the series of synthetic gallian-fluor amphiboles to identify the extent of Ga and Si ordering in the tetrahedral sites. Assignment of the peaks in the complex (super 29) Si MAS NMR spectra of pargasitic amphiboles is based on observations of the gradual change in peak intensity and position as well as by comparison with computer simulations of the relative intensities of the (super 29) Si MAS NMR spectra for the amphiboles along the compositional join. The (super 29) Si spectra agree best with models that allow Ga on both the T1 and T2 sites, which supports the previous cation distribution results obtained by Rietveld refinement of powder X-ray diffraction data. It was not possible, however, to discriminate between cation distribution models that allowed completely random mixing of Ga and Si vs. the presence of Ga-O-Ga avoidance on the tetrahedral sites. Comparison of the very high speed (super 71) Ga MAS NMR spectra (35 kHz) with the distribution of Ga in octahedral and tetrahedral sites shows that the ratio of tetrahedral to octahedral site occupancy is vastly overestimated from the NMR spectra due to the large quadrupolar effects of the asymmetrical octahedral site. The (super 23) Na MAS NMR spectra of tremolite and Ga-substituted pargasites show a shift to higher frequency and increasing peak width with Ga content that can be related to the reduction in magnetic shielding produced by the substitution of Ga for Si and Mg.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 84
Serial Issue: 7-8
Title: (super 23) Na, (super 29) Si, and (super 71) Ga MAS-NMR spectroscopy of synthetic gallian- fluor-amphiboles
Affiliation: University of Manitoba, Department of Geological Sciences, Winnipeg, MB, Canada
Pages: 1033-1040
Published: 199908
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 25
Accession Number: 1999-066009
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
Secondary Affiliation: Binghamton University, USA, United StatesFriedrich-Schiller-Universitaet, DEU, Federal Republic of Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 199922
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