--it isn't, to my knowledge.

Cyanocobalamin is a commercial preparation of B12; it is not the form in which B12 is naturally found in foodstuffs. The process of creating it involves bacterial fermentation and activated charcoal; it si added to make the cobalamin more chemically stable in air (for increased shelf life).

See:

http://en.wikipedia.org/wiki/Cyanocobalamin