In electron microscopic studies of Fischer‐Tropsch catalysts, an interesting phenomenon was observed in cobalt metal powder reduced from cobaltous oxide. The oxide particles sintered into larger smooth droplets of cobalt that were aggregated into thin hexagonal‐shaped platelets. X‐ray diffraction analysis showed the presence of the hexagonal crystal phase of cobalt. A possible explanation is that the aggregates are formed by forces similar to those operating in normal crystal formation, but of reduced magnitude insufficient to destroy the identity of the component particles.