Summary.Electronmicroscopical examination of (carbonyl) nickel powders consisting of particles a few microns in diameter has revealed two types of powder consisting respectively of (a) a mixture of irregularly shaped and cube‐shaped particles each with rough surfaces and(b)characteristically shaped particles with smooth surfaces. The form of the smooth surfaced particles could not be determined until evidence from the electron microscope was combined with evidence from the light microscope. It was then inferred that the smooth‐surfaced particles were single crystals in the form of icositetrahedra, probable indices of faces {5