what are its most common allotropes?
Amorphous carbon, graphite, and diamond
Carbon
lti-atomic structures with diverse molecular configurations called allotropes. The three relatively well-known allotropes of carbon are amorphous carbon, graphite, and diamond. 
describe carbon in covalent bonds and the importance of it It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds what are the characteristics of this element? Carbon is the sixth element, with a ground-state electron configuration of 1s2s2p, of which the four outer electrons are valence electrons. Its first four ionisation energies, 1086.5, 2352.6, 4620.5 and 6222.7 kJ/mol, are much higher than those of the heavier group-14 elements. where this element can be found in the earth? Earth's crust
wiki:1585189
Carbon [SEP] Allotropes
Atomic carbon is a very short-lived species and, therefore, carbon is stabilized in various multi-atomic structures with diverse molecular configurations called allotropes. The three relatively well-known allotropes of carbon are amorphous carbon, graphite, and diamond. Once considered exotic, fullerenes are nowadays commonly synthesized and used in research; they include buckyballs, carbon nanotubes, carbon nanobuds and nanofibers. Several other exotic allotropes have also been discovered, such as lonsdaleite, glassy carbon, carbon nanofoam and linear acetylenic carbon (carbyne). Graphene is a two-dimensional sheet of carbon with the atoms arranged in a hexagonal lattice. As of 2009, graphene appears to be the strongest material ever tested.