Delhaes, P. (2001). Polymorphism in carbons and parent materials. NATO Science series. 374: 3-27.

It has long been known that solid carbon can be found in various guises: besides the confirmation that the different forms of graphite and diamond are crystalline varieties of this element, new forms such as the carbynes the fullerenes and nanotubes, have recently been discovered. The cause of this rich polymorphism is analysed in the present review, and it will be shown that the propensity of carbon for forming different types of homopolar chemical bonds with variable coordination numbers which is also at the basis of classical orgmic chemistty (1).