Scoria

Scoria, loose, rubbly, pyroclast (solidified lava), ejected from a volcano. It is commonly glassy, fine-grained, and frothy in texture and full of vesicles (bubble-like cavities). These air pockets are formed by the expansion of gases and steam caught in the lava and by rapid cooling. Scoria (plural, scoriae) is produced by Strombolian volcanic activity (mild and frequent eruptions) or as frothy crusts on smooth lavas. Some scoriae resemble clinkers (stony residue) or cinders and are called volcanic cinder.

Scoria is most commonly grey or black, but is reddish-brown when oxidized; fresh scoria is iridescent. It is sharp-edged and angular and ranges in size from 64 mm (s in). Scoriae often build up into a scoria cone around a volcano’s central vent. Some cones reach up to 300 m (985 ft). Scoria is the basaltic equivalent of pumice, but is darker and more crystalline and too dense to float.