WHEN FINELY DIVIDED SHIRASU (PUMICE EJECTED FROM VOLCANOES AND THE SECONDARY DEPOSIT OF SUCH PUMICE) IS ROASTED AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 800* C., TO ABOUT 1200*C., THE VITREOUS PARTICLES CONTAINED IN SAID SHIRASU FOAM AND CONSEQUENTLY PRODUCE LIGHT-WEIGHT HOLLOW GLASS MICRO-SPHERES. THE HOLLOW GLASS MICROSPHERES SO PRODUCED ARE SUPERIOR TO CONVENTIONAL GLASS MICRO-SPHERES ESPECIALLY IN THEIR RESISTANCE TO HEAT AND CAN THEREFORE BE COMBINED WITH METAL, CARBON, AS WELL AS WITH CEMENT AND OTHER MATERIALS TO PRODUCE NOVEL LIGHTWEIGHT COMPOSITES.