According to Floris' answer in this link, diamonds are transparent as they have large band gaps while graphite is black as it is a conductor.

As electrical insulators generally have a large band gap, why aren't all insulators transparent?

  • 2
    $\begingroup$ If pure without inclusions, defects, scattering centers, and whatnot, they generally will be transparent. For example, sapphire (crystalline aluminum oxide) is wonderfully transparent, while alumina-based ceramics often are not (due to grain sizes and impurities). $\endgroup$ – Jon Custer Aug 17 '17 at 15:23
  • $\begingroup$ @JonCuster That sounds like a fairly complete answer. $\endgroup$ – WetSavannaAnimal Aug 18 '17 at 1:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.