Tamor, M. A. and K. C. Hass (1990). "Hypothetical superhard carbon metal." Journal of Materials Research 5(11): 2273-2276.

We describe a hypothetical new phase of carbon. The proposed structure is a rigid three-dimensional network with sp2 (threefold) coordination only. Tight-binding calculations indicate that the proposed material is a metastable metal significantly harder than diamond. Although it is unclear at present whether such a material can be produced in significant quantity, we speculate that it (and related structures) plays a role in the chemical vapor deposition of diamond films.