Fullerenes are one of only four types of naturally occurring forms of carbon (the other three are diamond, graphite and ceraphite). They are molecules composed entirely of carbon and take the form of a hollow sphere, ellipsoid, or tube. Sperical fullerenes are often called buckyballs (named after Buckminster Fuller, inventor of the geodesic dome), while cylindrical fullerenes are referred to as buckytubes or nanotubes.