We report on the first AFM images to our knowledge of the surface topo
graphy of fly-ash glassy spheres. Optically, two types of spheres are
observed: large ones (more than 100 mu m diameter) appear dark, small
ones (up to 10 mu m diameter) appear clear. Both were observed by AFM.
The light spheres do not appear to present much structure on their su
rface. In contrast, the dark spheres present numerous craters typicall
y of 300 nm diameter and 10 nm depth. Small particles, the largest of
about 110 nm and the smallest 13 nm in size, were also observed on top
of the largest glassy spheres.