A (57)Fe MOSSBAUER SPECTROSCOPIC STUDY OF SUGILITE, KNa(2)(Fe(3+),Mn(3+),Al)(2)Li(3)Si(12)O(30)

Geiger, C. A. (2009) A (57)Fe MOSSBAUER SPECTROSCOPIC STUDY OF SUGILITE, KNa(2)(Fe(3+),Mn(3+),Al)(2)Li(3)Si(12)O(30) Canadian Mineralogist, 47 (4). pp. 927-931. DOI 10.3749/canmin.47.3.927.

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Supplementary data:

Abstract

Sugilite, ideally KNa(2)(Fe(3+),Mn(3+),Al)(2)Li(3)Si(12)O(30), from the Wessels mine, Kalahari, South Africa, was studied using (57)Fe Mossbauer spectroscopy. The spectra confirm published electron-microprobe data and X-ray single-crystal results, which indicate that Fe(3+) is ordered at the A octahedral site. The magnitude of the quadrupole splitting, DEQ for Fe(3+) at both 84 K and room temperature is 0.00 mm/s. This value is very low for a silicate; reported DEQ values for octahedrally coordinated Fe(3+) are generally greater than 0.20 mm/s. Octahedron distortion, calculated from published X-ray-diffraction data, gives an octahedron-angle variance of 7 and a mean elongation of the octahedron of 1.002. This indicates nearly regular octahedral geometry, and hence a symmetric electric-field gradient around Fe(3+). A crystal-chemical interpretation for the regular octahedral geometry and the resulting low DEQ value for Fe(3+) in the Mossbauer spectrum of sugilite is that structural strain is largely "taken up" by weak Li-O bonds. They permit highly distorted LiO(4) tetrahedra, whose variance in the O-Li-O angle, 502, and mean elongation of the tetrahedron, 1.148, are among the largest observed values for inorganic crystal structures. Weak Li-O bonds allow the edge-shared, more strongly bonded Fe(3+)O(6) octahedra to remain regular in geometry.

Document Type: Article
Keywords: sugilite ring silicate Mossbauer spectroscopy iron hyperfine parameters site distortion double-ring silicates crystal-chemistry coordination
Research affiliation: Kiel University
Refereed: No
DOI etc.: 10.3749/canmin.47.3.927
ISSN: 0008-4476
Date Deposited: 22 Dec 2011 05:25
Last Modified: 08 Oct 2012 10:09
URI: http://eprints.uni-kiel.de/id/eprint/15777

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