“…An evaluation of the graphitization processes in the selected Oltrek samples can be carried out using the prominent D and G bands of carbon and defining specific Raman parameters that systematically change with the increasing metamorphism. [30][31][32][33][34][35][36][37][38][39] The first-and second-order Raman spectra have been correlated with changes in the structure of graphite; in their first-order Raman spectra, carbonaceous materials (CM) exhibit an intense band around 1,580 cm −1 (G), an additional band around 1,350 cm −1 (D1), and a weak band around 1,620 cm −1 (D2). In the second-order Raman spectra of graphite, the main observed bands are at 2,450 cm −1 , a doublet at 2,695 and 2,735 cm −1 (G′), and bands at 2,945 cm −1 (D1 + G), 3,176 cm −1 (2G), and 3,244 cm −1 (2D2) observed in samples excited with 514.5 nm wavelength.…”