S.A. Stout, J.J. Boon and W. Spackman, Molecular aspects of the peatification and early coalification of angiosperm woods, Geochim. Cosmochim. Acta 52, 405-414 (1988)
M. Nip, Chemical characterization of coals, coal macerals and their precursors: a study by analytical pyrolysis, Delft University of Technology, 1987-12-03