Graphene is another form of the element carbon. Its structure resembles a single layer of graphite. Graphene has a very high melting point and is very strong because of its large regular arrangement of carbon atoms joined by covalent bonds. Like graphite, graphene conducts electricity well because it has delocalised electrons that are free to move through its structure.
A nanotube resembles a layer of graphene, rolled into a tube shape. Nanotubes have high tensile strength, so they are strong in tension and resist being stretched. Like graphene, nanotubes are strong, and they conduct electricity because they have delocalised electrons.
Buckyballs are spheres or squashed spheres of carbon atoms. They are made up of large molecules but do not have a giant covalent structure. Weak intermolecular forces exist between individual buckyballs. Little energy is needed to overcome these forces, so substances consisting of buckyballs are slippery and have lower melting points than graphite or diamond.