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Chemical and structural evidence for (super [4]) <--> (super [4]) Si substitution in natural tourmalines


Because tourmaline is the most common boron-bearing mineral, the crystal chemistry of B in the phase is of fundamental importance to understanding the boron budget in the Earth. Until recently, the presence of (super [4]) B as a substituent in the tourmaline tetrahedral (T) ring was unrecognized. However, a study of an Austrian olenite has shown that the substitution is not only possible but can occur in amounts up to B (sub 1.00) per T (sub 6.00) . Through Magic-Angle-Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy, it was recently shown that (super [4]) B in tourmaline can be identified by its spectroscopic signature. This study characterizes the structural response to small (<0.50 apfu) amounts of substituent (super [4]) B. Two tourmaline samples ( (super [4]) B0.28, (super [4]) B0.37 by chemical analysis) that have been demonstrated by MAS-NMR to contain (super [4]) B were analyzed by single-crystal X-ray techniques. It was found that reasonable agreement is obtained between (super [4]) B content as determined by Secondary Ion Mass Spectrometry and X-ray site refinement, although the X-ray refinement significantly overestimates (super [4]) B (by 3sigma ) in one sample. The response of the tourmaline atomic arrangement to the incorporation of substituent (super [4]) B is subtle, perhaps explaining the lack of previous recognition of the substitution. The P-T-X conditions required for the substitution are not known, but are being studied by mineral researchers; it has been observed that all of the (super [4]) B-bearing tourmalines discovered to date contain little or no Mg on the octahedral sites.

ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 13
Serial Issue: 4
Title: Chemical and structural evidence for (super [4]) <--> (super [4]) Si substitution in natural tourmalines
Affiliation: Miami University, Department of Geology, Oxford, OH, United States
Pages: 743-747
Published: 200108
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 14
Accession Number: 2001-065611
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
Secondary Affiliation: Mount Holyoke College, USA, United States
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute.
Update Code: 200120
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