Safora rwbe (MIXER)

Ah, a very good question. The answer truly depends on which form, or allotrope, of carbon you mean.

Take diamond. Its atoms are locked in a very rigid crystal structure. This creates an enormous energy gap—the 'band gap'—that electrons must cross to conduct electricity. The gap is simply too large. Voilà, diamond is a superb insulator.

Graphite, on the other hand, is completely different. Its layered structure allows electrons to move quite freely, making it a conductor.

A semiconductor like silicon has a band gap that is small enough. It is 'just right' to allow for controlled conductivity. Carbon, in its most common forms, is either at one extreme or the other, an insulator or a conductor.