Microanalysis of barkinite from Chinese coals of high volatile bituminous rank

Permian high volatile bituminous barkinite-rich coal from China has been evaluated petrographically and analyzed by electron microprobe and micro-FTIR techniques. The analyzed samples varied in vitrinite reflectance from 0.65% to 0.73%, and the corresponding reflectance of barkinite ranged from 0.19% to 0.23%. Compared to the associated vitrinite, barkinite had a higher carbon and lower oxygen content in all samples. It had stronger aliphatic CHx absorbance at 2800–3000 and 1450–1460 cm− 1 and less intense both aromatic C = C ring stretching vibration at ~ 1600 cm− 1 and aromatic CHx out-of-plane deformation at 700–900 cm− 1. Micro-FTIR revealed large variations in the aliphatic group intensities within barkinite, suggesting its varying oil generation potential. Air oxidation of barkinite over a 6-month period resulted in rapid consumption of aliphatic groups and the formation of oxygenated functional groups.