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*'''Scoria''' is a vesicular (bubbly) glassy lava rock of basaltic to [[andesitic ]] composition ejected from a vent during [[explosive eruption]]. The bubbly nature of scoria is due to the escape of volcanic gases during eruption. Scoria is typically dark gray to black in color, mostly due to its high [[iron ]] content. The surface of some scoria may have a blue [[iridescent ]] color; [[oxidation ]] may lead to a deep reddish-brown color. (USGS<ref>[http:/VHP) /vulcan.wr.usgs.gov/Glossary/volcano_terminology.html Glossary of Volcano and Related Terminology]</ref> *Scoria forms when blobs of gas-charged lava are thrown into the air during an eruption and cool in flight, falling as dark volcanic rock containing cavities created by trapped gas bubbles. (Clynne, et.al., 1998) <ref>[http://vulcan.wr.usgs.gov/Glossary/volcano_terminology.html Glossary of Volcano and Related Terminology]</ref>