Single sheets of graphene can also be rolled up to create carbon nanotubes. These form when carbon compounds are immersed in intense flames or electrical arcs. Making it likely that even cavemen "made" carbon nanotubes in their campfires. The hard part is sorting the nanotubes from all the other forms of carbon created at the same time.
Nanotubes can be formed by rolls of single or double sheets of graphene. Further, these sheets can be joined so that carbon rings circle the nanotube ("normal") or spiral up it ("chiral"). To alternate between normal and chiral single-walled nanotubes, click this button:
Pi electrons move differently in "normal" vs. "chiral" nanotubes, giving them different electrical conductivity.