Natural carbon black (Oltu-stone) from Turkey: a micro-Raman study

This study focuses on the characterization of a carbon black material from the Oltu-Erzurum region (traditionally called in Turkey "Oltu-stone" or "black-amber"), which is of interest in several fields, among these archaeometry and jewellery. Raman spectra were recorded between 50 and 3200 cm(-1): measurements in a wide spectral range are the basis for effective characterization and identification with respect to analogous materials. Correlations between the spectrum and the structure are discussed: two higher energetic Raman peaks at 1346 and 1585 cm(-1) are characteristic of the crystalline carbon regions, whereas the weaker ones at 2654 and 2904 cm(-1) are ascribed to amorphous carbon regions on the Oltu-stone surface. In addition, the enhanced background between 250 and 400 cm(-1) could be associated with the presence of pyrite.