Raman spectroscopic identification of B-free and B-rich kornerupine (prismatine)

Washington University, Department of Earth and Planetary Sciences, Saint Louis, MO, United States

This is the first application of Raman spectroscopy to the characterization of the kornerupine group of borosilicate minerals. Raman microprobe spectra were collected from approximately 100 to approximately 4000 cm (super -1) from 13 samples of kornerupines (from different localities) containing a wide range of boron content (0.02 to 0.84 boron atoms per formula unit of 21.5 O atoms). The Raman spectra of the kornerupines are consistent with the structure of the mineral as determined by X-ray diffraction (XRD) analysis, which locates the boron in a tetrahedron at the center of a trimer of corner-sharing tetrahedra and with the presence of only hydroxylions (OH) but no molecular water (H ₂ O). Two of the Raman vibrational modes of kornerupines (at approximately 803 Delta cm (super -1) and at approximately 884 Delta cm (super -1) ) are sensitive to the presence of boron, and their relative intensities can be used to discriminate between kornerupine and prismatine. Based on the intensities of those boron-sensitive bands, the Raman spectroscopic technique could potentially provide a semi-quantitative measure of the boron content of kornerupine.

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