The fullerenes, discovered in 1985 by researchers at Rice University, are a family of carbon allotropes named after Buckminster Fuller. They are molecules composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are sometimes called buckyballs, the C60 variant is often compared to a typical white and black soccer football. Cylindrical fullerenes are called buckytubes. Recently discovered is the "buckyegg", by researchers at UC Davis. Fullerenes are similar in structure to graphite, which is composed of a sheet of linked hexagonal rings, but they contain pentagonal (or sometimes heptagonal) rings that prevent the sheet from being planar.