H 0939 (OTTO) Holmium powder, -200 mesh, 99.9% Cas no 7440-60-0 - used in the same way as some other rare earths in certain laser and glass-colorant applications. H 0939 (OTTO) Holmium powder, -200 mesh, 99.9% Cas no 7440-60-0 - used as a burnable poison in nuclear reactors.