Alumino-silicate Cenospheres/Hollow Ceramic Microspheres Cenosphere are light weight,inert,hollow speres of Silica and Alumina filled with gas which naturally occurs in the combustion of coal during the generation of electric power.The properties are same as manufactured sphered products.Thus it is also called as Glass Beads,Hollow Ceramic Sphere or Microspheres. Size range from 10 to 600 microns, 35mesh, 40mesh, 48mesh, 50mesh, 80mesh, 100mesh, 115mesh, 150mesh, 200mesh. Colors range from white to light gray.