Fourier transform infrared (FTIR) spectra of lignite and humic clay samples, collected from 2 boreholes located at Apofysis-Amynteo lignite deposit, NW Greece, as well as their insoluble organic matter, obtained by Soxhlet extraction with dichloromethane, were recorded between 400 and 4,800 cm(-1). In the same way, FTIR spectroscopy was used to study a xylite sample from Vevi xylite basin (north of Apofysis-Amynteo lignite deposit) and its chars, which are the solid products of pyrolysis, at 3 final fixed temperatures: 400degreesC, 600degreesC, and 800degreesC. In the Apofysis-Amynteo samples, oxygen-containing structures were observed in the 1,800-1,000 cm(-1) zone, aliphatic hydrogen in the 2,950-2,700 cm(-1) zone, aromatic out-of-plane structures in the 900-670 cm(-1) zone, and hydroxyl groups in the 3,400-3,600 cm(-1) zone. A great abundance of C=O and C-O-R structures in the 1,800-1,000 cm(-1) region were noticed, while clay and silicate minerals were identified in the 400-600 cm(-1) and 3,600-3,800 cm(-1) zones. In the IR spectra of the initial xylite sample BEX, the major quantity of H2O is at a wave number of 3,400 cm(-1). A strong peak at 1,032 cm(-1) in the xylite sample is evidence of the presence of phenolic and alcoholic C-O bonds as well as C-O-C bonds with aliphatic or aromatic carbons. The 800degreesC char, at the same wave number, presents only a weak peak.