Wiktionary
maceral
n. A component of coal or oil shale.
Wikipedia
Maceral
A maceral is a component, organic in origin, of coal or oil shale. The term 'maceral' in reference to coal is analogous to the use of the term ' mineral' in reference to igneous or metamorphic rocks. Examples of macerals are inertinite, vitrinite, and liptinite.