1.3 Scoria and Volcanic Cinder. Scoria (larger than 1 in (2·5 cm) in size) and volcanic cinder (smaller) are cellular, frothy products of explosive mafic volcanism—erupted as bombs, blocks, lapilli, volcanic gravel, or lava flows. Much of the material is lava forcefully ejected from the vent, vesiculating as volcanic gases expand and are ...