Pentagonal- and hexogonal-shaped building block precursors provide a novel, high-yield method for the preparation of carbon onions and nanosized graphite particles. A reaction of hexachlorocyclopentadiene (C5Cl6) with sodium (see Figure) offers carbon onions with 8-50 spherical and elliptical shells. The same reaction with hexachlorobenzene (C6Cl6) results in a mixture of graphite crystallites. [GRAPHICS]