PUMICE A highly porous igneous rock, usually containing 67 – 75% SiO2 and 10 – 20% Al2O3, glassy texture.  Potassium, sodium, and calcium are generally present.  Insoluble in water, not attacked by acids. Occurrences:  USA (Arizona, Oregon, California, Hawaii, New Mexico), Italy, New Zealand, Greece. Grade:  Lump, powdered coarse, medium, fine; NF, technical. Use:  Concrete aggregate, heat and sound insulation, filtration, finishing glass and plastics, road absorbents, support for catalysts, dental abrasive, adherent for uncured rubber products, possible substitute for asbestos.