Italian volcanoes spilled out streams of molten rock called lava, a word possibly derived from lavare, "to wash", in the sense of a torrent of water. Material ejected into the air came down as lapilli, "little stones", scoria, "slag", or pumice, "foam". We still use these words today.
Lavas reveal their origin by certain distinctive textures: a dense, fine-grained, or even glassy appearance, riddled with spongy-looking bubble holes formed by gas trapped before it could escape. Scoria and pumice are nearly more bubbles than stone, and are surprisingly light in weight. Volcanic ash is little more than tiny shards of dirty glass and broken crystals.