durain

durain, macroscopically distinguishable component, or lithotype, of coal characterized by a hard, granular texture and composed of the maceral groups exinite and inertinite as well as relatively large amounts of inorganic minerals. Durain occurs as thick, lenticular bands, usually dull black to dark grey in colour. Durain is thought to have formed in peat deposits below water level, where only exinite and inertinite components resisted decomposition and where inorganic minerals accumulated from sedimentation. See also clarain; fusain; vitrain; maceral.