Graphite is one of the softest known materials while diamond is one of the hardest. Carbon, as microscopic diamonds, is found in some meteorites. Diamonds are also recovered from the ocean floor off the Cape of Good Hope. In combination, carbon is found as carbon dioxide in the atmosphere of the earth and dissolved in all natural waters. Coal, petroleum, and natural gas are chiefly hydrocarbons.
Carbon is unique among the elements in the vast number of variety of compounds it can form.
While silicon might take the place of carbon in forming a host of related compounds, it is not possible currently to form stable compounds with very long chains of silicon atoms. Both values are quoted on the Pauling scale. The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. This section gives some data for naturally occurring isotopes.