When the bubbles are tiny and closely packed, a lightweight stone called pumice is formed. Any kind of lava may turn into pumice, but most of it develops in rhyolites. Pumice is used commercially for cleaning and polishing wood, metal, and other surfaces. More recently it has found use in precast masonry, poured concrete, insulation, acoustical tile, and plaster. Rhyolite pumices are white.
Andesite pumices are usually yellow or brown.
Basaltic pumices are black. Commercially useful pumices are found in the Canary Islands, Iceland, Italy, Hungary, Greece, New Zealand, and Germany. In the United States it is mined in the Rocky Mountains, on the West Coast, and in Hawaii. Andesites, which are named for the Andes Mountains, are a large family of rocks found in nearly all volcanic areas. Basaltic eruptions can produce two different types of flow.