Pumice 7 : Low-density fragments of silicate glass (generally of dacitic to rhyolitic composition) containing few crystals but a large fraction of gas bubbles (voids) due to exsolution of gas from magma during eruption. See: Scoria
Peter Bormann, Keiiti Aki, William H. K. Lee, and Johannes Schweitzer (Compilers and Amenders), Glossary of Terms Interest to Earthquake and Engineering Seismologists (Version 1), Publication records from external use of GFZ scientific infrastructure, Germany 2011. http://gfzpublic.gfz-potsdam.de/pubman/item/escido c:56137:3/component/escidoc:56143/Glossary_rev1.pd f, (ND/ Erthq - Amer) {980}