Raman spectroscopic quantification of tetrahedral boron in synthetic aluminum-rich tourmaline
Raman spectroscopic quantification of tetrahedral boron in synthetic aluminum-rich tourmaline
American Mineralogist (June 2021) 106 (6): 872-882
- alkali metals
- alkaline earth metals
- Alps
- aluminum
- Austria
- B-11/B-10
- beryllium
- boron
- Central Europe
- coordination
- crystal structure
- Eastern Alps
- electron microscopy data
- electron probe data
- Europe
- experimental studies
- fluid phase
- high pressure
- ion probe data
- isotope fractionation
- isotope ratios
- isotopes
- Koralpe Range
- lithium
- mass spectra
- metals
- polyhedra
- pressure
- quantitative analysis
- Raman spectra
- ring silicates
- SEM data
- silicates
- spectra
- stable isotopes
- synthetic materials
- tetrahedra
- tourmaline group
- X-ray diffraction data
The Raman spectra of five [4]B-bearing tourmalines of different composition synthesized at 700 degrees 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 a tracer of mass transfer processes.
