In the present work nucleation and growth of diamond by chemical vapor deposition (CVD) on highly oriented pyrolitic graphite (HOPG) and glassy carbon (GC) substrates have been investigated. These carbon substrates represent generic forms of well‐characterized ordered and disorderedsp2bonded carbon materials. The nature of the precursor to diamond CVD is assessed by studying nucleation and growth on substrates abraded with hard powders whose debris may act as initial growth centers, e.g., diamond andc‐BN, and hard powders onto which diamond CVD does not grow heteroepitaxially, e.g., alumina. Based on our experimental results it is concluded that the precursor to diamond nucleation may be debris left after the abrasion process and/or damage created preferentially on graphitic prism planes. A higher density of such damaged prism planes on GC than on HOPG resulted in a larger nucleation density on the former. Different morphologies of single particles deposited on HOPG and GC were found: well faceted on the former, and ball‐like on the later as determined by scanning electron microscopy. This difference is explained on the basis of a larger concentration of active carbon species present at the GC surface as compared to the HOPG surface. The additional source of carbon is from etching of the GC and HOPG substrates which, under the diamond CVD conditions used in the present study, is twice higher for GC. The thermal stability of continuous films deposited on HOPG is better than those deposited on GC. The presence of different carbon phases in the deposited material was investigated by micro‐Raman and scanning‐Auger electron spectroscopies. ©1995 American Institute of Physics.