I would say that is a nice jasper tool of some sort, and has a really cool fresh water patina on it. We find similarly formed pieces down my way, and I am not sure what to make of them? It could be that the material they were using could not have those lumps, bumps or stacks removed, so they just worked around them and ended up with knives, scrapers or piercing tools with thick bases. Or it could be that some were intentionally formed that way, and possibly were used as wedges in splitting wooden shafts etc. ? I supposed that if a wedge tool like that were struck on the thick end with a wooden stick or mallet, that it probably wouldn't leave a visible mark on every piece?