Scoria is a dark-colored igneous rock with abundant round bubble-like cavities known as vesicles. It ranges in color from black or dark gray to deep reddish brown. Scoria usually has a composition similar to basalt, but it can also have a composition similar to andesite.

Many people believe that small pieces of scoria look like the ash produced in a coal furnace. That has resulted in particles of scoria being called “cinders” and the small volcanoes that erupt scoria to be called “cinder cones.”