The exception is graphite, a form of carbon. Although a non-metal, it conducts electricity. With slight variations in its form, it can oscillate between being a conductor and an insulator.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/graphite-and-its-split-personalities
[2] http://admin.indiaenvironmentportal.org.in/category/author/vibha-varshney
[3] http://admin.indiaenvironmentportal.org.in/category/newspaper/deccan-herald-bangalore
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/science-and-technology
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/research