... granularity diameter is about 1 mm , Hollow glass micropheres is a hollow ball collected from coal powder,its coloure ... is light grey,thin wall,hollow,light weight.Volume weighs is 250----450kg ... contains SiO2 and Al2O3, with fine particles ,hollow, high strength and durable, resistant to temperature etc.It ... —200 mesh,over 200 mesh Hollow Glass Microspheres Collected From Coal Powder