TNT (trinitrotoluene), an explosive, occurs naturally as an intermediate
product of the decomposition of certain types of organic matter.
Why does it not explode?
TNT is a solid; as an intermediate it usually is in solution form. TNT is not sensitive to shock and friction AND although the explosive is highly exothermic, it has a high activation energy. You can read more about it here.
http://en.wikipedia.org/wiki/Trinitrotoluene