Inertinite refers to a group of partially oxidized organic (mainly plant) materials or fossilized charcoals, all sharing the characteristic that they typically are inert (i.e., not altered) when heated in the absence of oxygen.
The presence of inertinite in this context is significant in the geological record, as it signifies that wildfires may have occurred at the time that the host sediment was deposited.
[3][4] It can also be an indication of oxidation due to atmospheric exposure or fungal decomposition during deposition.
They differ in that semifusinite displays a folded texture compared to vitrinite, which generally maintains its composed structure.
Inertinites also display higher reflectance than vitrinite, except when approaching an anthracitic or graphite state.