I believe its a glob of bitumen. Sometimes bitumen will collect at suboceanoic seeps and roll for centuries along a shallow shoreline where an long shore current just turns em into a cruller. What gave me a clue is the "cut mark" along the side of the chunk. A rock wouldnt leave a gut like that (except bitumen and certin coals). I dont believe its a coal because coal doesnt usually hve those kinds of inclusions.
If you can peel a teeny piece off and try to set it aflame on a dish, if it melts and begins to smoke or burn, its a bitumen sample.
Are you in the US? along the Calif or Gulf oats?