cinder

Cinders are fragments of pyroclastic rock ejected during volcanic eruptions. They accumulate around a volcanic vent, forming a conical hill with a crater at the top, known as a cinder cone. These cones are typically formed from explosive eruptions of mafic or intermediate lavas and are often found on the flanks of shield volcanoes.12

The size of cinders can range from 2 mm to about 64 mm (2.5 inches). Cinder cones are generally inclined at about 30°, the angle at which loose cinders can remain stable. While they can be relatively small, some can reach heights of several hundred meters. Despite being composed of loose material, cinder cones can be surprisingly enduring features due to their high permeability, which allows rainwater to sink in rather than causing erosion.31