Peds bounded by undulating surfaces having a luster or shininess constitute the subsoil of many major soil types worldwide. Characteristics of ped surfaces, such as presence or absence of luster, color, texture, and porosity, are often used as diagnostic criteria for clay coatings at a high category level in soil classification. There is, however, little agreement on either the formation or the physical nature of undulating lustrous ped surfaces. In particular, soil micromorphological studies have demonstrated that clay coatings apparent on ped faces during field examination are often not detectable when using soil thin sections and optical microscopy. Scanning electron microscopy of fractures across the undulating lustrous surfaces of peds from 30 layers of a wide variety of soil types (Alfisols, Mollisols, Vertisols, Ultisols and Oxisols) indicates that these peds were covered by depositional clay coatings. In 12 of the thirty soil layers, these clay coatings were