Carbon atoms can join together to form hollow cages of various shapes called fullerenes. The structure is based on hexagonal rings similar to those in graphite, with some pentagonal rings.Buckminsterfullerene, C60, is a form (allotrope) of carbon which is a dark solid at room temperature. Fullerenes could be used for drug delivery to the body, lubricants or catalysts.Cylindrical fullerenes are called carbon nanotubes. They form long cylinders with high tensile strength and high electrical conductivity.