| − | *A light-colored, frothy volcanic rock, usually of dacite or rhyolite composition, formed by the expansion of gas in erupting lava. Commonly perceived as lumps or fragments of pea size and larger but can also occur abundantly as ash-size particles. (Foxworthy and Hill, 1982)
| + | A light-colored, frothy volcanic rock, usually of [[dacite]] or [[rhyolite]] composition, formed by the expansion of gas in erupting [[lava]]. Commonly perceived as lumps or fragments of pea size and larger but can also occur abundantly as ash-size particles.<ref>[http://vulcan.wr.usgs.gov/Glossary/volcano_terminology.html Glossary of Volcano and Related Terminology (Foxworthy and Hill, 1982)]</ref> |