Transmission electron microscopy of polycrystalline natural diamond (carbonado) revealed the existence of voidites. These were different to the voidites in type-Ia natural diamonds, not only with regard to shape but also content and origin. Other defects were also observed, such as dislocation networks, micro-twins and large-angle grain boundaries. It was concluded that voidites could be formed as a sink for impurities; not only within diamond grains but also between grains with a closely-related orientation. In the former case, the nucleation of voidites along dislocation lines was preferred while, in the latter case, planar-like voidites formed so as to permit direct bonding between diamond grains.

J.H.Chen, D.Bernaerts, J.W.Seo, G.Van Tendeloo, H.Kagi: Philosophical Magazine Letters, 1998, 77[3], 135-40