Chemical and spectroscopic characterization of tourmalines from the Mata Azul pegmatitic field, Central Brazil

Abstract

This study characterizes natural black, blue, dark green, light green and pink tourmalines from granitic pegmatites of the Mata Azul Pegmatitic Field in central Brazil. The differences were assessed by applying electron-microprobe analysis as well as Mössbauer and optical spectroscopies. Mineral chemistry data show an increasing Mn/(Mn + Fe) atomic ratio as follows: black (0.01-0.02), blue (0.04-0.05), dark green (0.09-0.21), light green (0.33-0.42) and pink (0.68-1.00). The Mössbauer spectroscopy results show the presence of Fe 2+ (doublets with isomer shift (δ): 1.04-1.15 mm/s) for the black, blue, light green and dark green tourmalines. Fe 2+ is found in three different environments that are identified by quadrupole splitting (Δ) of 2.38-2.49 mm/s for the first, Δ = 2.13-2.34 mm/s for the second, and Δ = 1.54-1.71 mm/s for the third. The black sample spectrum has an additional fourth doublet (δ = 0.78 mm/s, Δ = 1.22 mm/s) that is assigned to an electron delocalization between Fe 2+ and Fe 3+. In the studied samples, the black color results most likely from high absorbance in all the visible spectra caused by Fe

Multi-technique characterization of colored gem tourmalines

“…Generally, the color in natural tourmalines can be correlated to the presence of Mn (Mn 2+ , Mn 3+ ), Fe (Fe 2+ , Fe 3+ ), and Ti (Ti 4+ ) elements within the Y-site of the TM unit or to the existence of impurity defects and charge transfer between cations. In the case of the TM1 sample, a high concentration of Mn with respect to other elements (see Table 1) indicates the observed reddish coloration can be reasonably attributed, in agreement with what was already reported in the literature [16], to the presence of Mn atoms occupying the Y sites of the crystal structure, following Mn ↔ [Li1.5Al1.5] end-member substitutions. In this case, the more violetish color of TM1 suggests a gradual conversion of Mn 2+ into Mn 3+ , consequently a prolonged exposure to natural radiation.…”

Identification of Pheophytin a and Hydroxy Pheophytin a from Rang Chuet (Thunbergia laurifolia Linn.) as Potent NQO-1 Inducers in Liver Cells

“…In this study, the IC 50 values of the RC crude extract and its fractions were determined and found to be above 2 mg/mL for all but Fraction 1 (F1) in the AML12 cell line (Table 2). High IC 50 values indicate a low level of cytotoxicity, suggesting the chemoprotective potential of most RC constituents [34]. While F1 exhibited an IC 50 value slightly below 2 mg/mL in AML12 cells, the difference was not statistically significant (p < 0.05).…”

Iron-bearing to iron-rich tourmalines from granitic pegmatites of the Murzinka pluton, Central Urals, Russia

“…The Mössbauer spectroscopy is useful for the examination of site occupancies and valence state of Fe in tourmaline species, thus, allow to estimate the Fe 3+ /Fe tot and Fe 3+ /Fe 2+ ratios (Dyar et al, 1998;Oliveira et al, 2002;Silva et al, 2018). The Mössbauer spectra were measured for fourteen tourmaline samples and their parameters are given in Table 3; the representative spectra are shown in Fig.…”

“…5 for legend. et al, 1998;Oliveira et al, 2002;Silva et al, 2018). Mössbauer spectra were measured for 14 tourmaline samples and their parameters are given in Table 3 with representative spectra shown in Fig.…”