Carbon allotropes:

All carbon allotropes are solids within normal circumstances with graphite being the most thermodynamically stable form. They are chemically resistant and need high temperature to react even with oxygen. The very much common oxidation state of carbon in inorganic compounds is +4, whereas +2 is found in carbon monoxide and another transition metal carbonyl complexes. The major sources of inorganic carbon are limestones, dolomites and carbon dioxide, but important quantities take place in organic deposits of coal,  oil and methane clathrates. Carbon forms more compounds as compared to any another element, with almost ten million pure organic compounds explained to date, which in turn is a tiny fraction of such types of compounds which are theoretically possible under standard conditions.