Raman spectroscopy of weathered shungites

Raman spectroscopy has proven to be a useful tool for the study of carbonaceous material (CM). This method is used to distinguish various types of CM and to study the evolution of Raman spectra characteristics of CM during metamorphic transformations. In the present study, we applied the Raman spectroscopy and electron diffraction methods to investigate the evolution of structural ordering of CM of shungite rocks, Karelia (Russia), during weathering. The studies of the CM structure evolution during weathering are rare and ambiguous. The Raman spectra of weathered shungites are characterized by increase of FWHM-D1, that is accompanied by the decrease of intensity-based ratio R1=I-D/I-G and the change of the intensity of the bands in second-order region. The Raman spectral data indicate that weathering results in the alteration of both intralayer and interlayer ordering of shungites, but there are some peculiarities for the shungites subjected to the various types of weathering. The present study establishes that the Raman spectra characteristics of weathered shungites can be used as the indicators of weathering for CM from various carbon-bearing rocks. Copyright (c) 2017 John Wiley & Sons, Ltd.