A brown hard fungus that resembles charcoal briquette, and can actually be used as tinder to start fires. The fungus is ball-shaped, with a hard, friable, shiny black fruiting body 2 to 7 centimeters wide. It resembles a chunk of coal, which gives it several of its common names, including coal fungus and carbon balls. The flesh of the fungus is purple, brown, or silvery-black inside, and is arranged in concentric layers. Each layer represents a season of reproduction.
It lives on dead and decaying wood, especially on felled ash trees.