Coal-derived pitchcoke, although it exhibits a pregraphitic microstructure, has often a lower graphitizability than petroleum coke. Fractions of coal tar pitches (obtained by extraction or filtration) may form cokes with needle-like structures and have an improved graphitizability. The usually lower graphitizability compared to petroleum coke is due to an inhibition of mesophase growth because of chemical and physical differences of the cokes.
PAC, 1995, 67, 473
(Recommended terminology for the description of carbon as a solid (IUPAC Recommendations 1995))
on page 485