Is diamond a conductor or insulator?

Answer 1

No, Diamond is considered an electrical insulator. Source: http://en.wikipedia.org/wiki/Thermal_conductivity (first paragraph under 'Examples')
Yes, diamonds are conductive. In fact their conductivity is just 1 of the things that sets them apart from other gems. Basically, this means that diamonds have the ability to conduct heat. Their conductivity is actually relatively high compared to that of glass or gold.

Answer 2

No.

That's because it has no delocalised electrons in its structure. No delocalised electrons means no current, since current = flow of electrons.

(extra info)

But its isotope graphite does conduct electricity because an extra electron from the p orbital delocalised all over, in between the sheets of hexagons in its structure.

Buckminsterfullerene also has delocalised electrons (but no as many per C atom as graphite) making it electrically conductive too.

Answer 3

Diamond is an insulator because it is composed of carbon atoms arranged in a tight lattice structure that restricts the movement of electrons, preventing them from flowing freely to conduct electricity.

Answer 4

Diamond is a great conductor of heat, but a poor conductor of electricity.

Answer 5

Diamond is a good thermal conductor. But it is an excellent electrical insulator.