Raman spectral characterization of dispersed carbonaceous matter in decorative crystalline limestones

Crystalline limestones (marbles) is a metamorphic rock that is widely used in the construction of buildings and in the manufacturing of statues. Along with dominant carbonates, marbles often contains carbonaceous matter resulting in a more or less grey colour. The Raman spectra of metamorphosed carbonaceous material (CM) were obtained in so-called graphitic marbles from several sites in the Bohemian Massif (Czech Republic). Frequencies of the major Raman bands and spectroscopic parameters such as O- and D-peak width and D/O intensity ratio were determined to characterize the various types of CM. Three types of Raman spectra allowed the discrimination between (1) well-ordered CM–graphite of high-grade regional metamorphosed marbles, (2) CM of contact metamorphosed marbles and (3) amorphous organic compounds as “disordered” CM of low-grade regional metamorphosed marbles. Raman microspectrometric analysis revealed the coexistence of carbonaceous particles exhibiting different degrees of graphitization within one marble sample. The structural state of the CM reflects the conditions of the contact or regional metamorphism and can be described by nondestructive Raman spectroscopy. For the first time, Raman spectra measured on reduced CM grains permitted one to distinguish marbles of different origin and propose their utilization in the provenance determination.