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Tourmaline, high pressure, synthesis, tetrahedral boron, Raman, SIMS, Lithium, Beryllium and Boron: Quintessentially Crustal
Abstract:
The Raman spectra of five [4]B-bearing tourmalines of different composition synthesized at 700°C/4.0 GPa (including first-time synthesis of Na-Li-[4]B-tourmaline, Ca-Li- [4]B-tourmaline and Ca-bearing -[4]B-tourmaline), reveal a strong correlation between the tetrahedral boron content and the summed relative intensity of all OH-stretching bands between 3300–3430 cm-1. The band shift to low wavenumbers is explained by strong O3-H...O5 hydrogen bridge bonding. Applying the regression equation to natural [4]B-bearing tourmaline from the Koralpe (Austria) reproduces the EMPA-derived value perfectly [EMPA: 0.67(12) [4]B pfu vs. Raman: 0.66(13)[4]B pfu]. This demonstrates that Raman spectroscopy provides a fast and easy-to-use tool for the quantification of tetrahedral boron in tourmaline. The knowledge of the amount of tetrahedral boron in tourmaline has important implications for the better understanding and modeling of B-isotope fractionation between tourmaline and fluid/melt, widely used as tracer of mass transfer processes.
