Molecular Structure of Different Forms of Carbon
Carbon can form very different substances, all by itself, depending on the way its atoms bond. In diamond, one of the hardest substances known to man, carbon atoms are fixed in a rigid 3-D network of covalent bonds. In graphite, a soft and slippery manifestation of carbon, strong covalent bonds exist in layers. (and only a weak force exists between the layers, allowing them to move, resulting in graphite being a lubricant)
In addition to graphite and diamond, there are some fairly new carbon structures on the scene, including the 'buckyball,' which consists of 60 carbon atoms, bound together in hexagonal and pentagonal shapes ,to form a hollow sphere. There are also carbon materials, called Fullerenes, which are being constructed to form larger spheres, ellipsoids, and nanotubes to be used as microscopic filters and catalysts.