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Heavy, dark, glassy igneous rock that contains many bubblelike cavities. Foamlike scoria, in which the bubbles are very thin shells of solidified basaltic magma, occurs as a product of explosive eruptions (as on Hawaii) and as frothy crusts on some lavas. Other scoria, sometimes called volcanic cinder, resembles clinkers, or cinders from a coal furnace.
This entry comes from Encyclopædia Britannica Concise. For the full entry on scoria, visit Britannica.com.