pumice - typical white pumice that floats like a duck - Unit of 5 student specimens

Ejected in a blast from a volcanic vent, pumice hardens as it flies through the air, trapping bubbles of gas and steam. It is light enough to float on water - these specimens will all float. The composition of this silica rich volcanic rock is similar to that of obsidian or granite. Pumice is commercially used as an abrasive.  This pumice is from the Coso Range in California. The area is geologically active, with a nearby geothermal plant on the Naval Air Weapons Test Center producing electricity from steam. The Navy sells surplus electricity into the commercial grid. This pumice is closely associated with rhyolite porphyry, blocks of which are buried in the pumice. Both have a similar silica-rich composition - rhyolite lava flows reluctantly because the silica makes it viscous. This same viscosity prevents easy fountaining of lava, so pressure builds up and a silica-rich eruption is explosive.  The silica poor equivalent of pumice would be scoria or volcanic cinder. Also full of entr