The elementary organic constituent of coal, recognizable at a microscopic level and made up of the remains of plant materials existing at the time of peat formation.

There are three main maceral groups, recognized on the basis of their physical appearance:

  • Vitrinite, formed mainly from the remains of trunks, branches, leaves, roots and stems of land plants. This is the principal group in most coals.
  • Exinite, made up of small organic particles such as algae, spores and cuticles, and is fairly high in hydrogen and volatiles.
  • Inertinite, which have high carbon and low hydrogen contents.