Inertinite

Inertinite is oxidized organic material or fossilized charcoal. It is found as tiny flakes within sedimentary rocks. The presence of inertinite is significant in the geological record, as it signifies that wildfires occurred at the time that the host sediment was deposited. It is is also an indication of oxidation due to atomospheric exposure or fungal decomposition during deposition. Inertinite is a common maceral in most types of coal. The main inertinite submacerals are fusinite, semifusinite, micrinite, macrinite and funginite. The most common type of inertinite maceral is fusinite.

The optical properties of semifusinite are very similar to those of vitrinite. They differ in that inertinite is black, whereas vitrinite is brown, and inertinite also has a higher reflectance than vitrinite.