Fossil or just a rock?

[rock]

I found this a while back in a river. Its limestone I do believe but thought it was strange shape and very heavy for its size. So is it a fossil or just a rock? Top, side, and back shots.

 

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[Harry Pristis]

If it's a fossil, it's not something I recognize.

 

[Ninjafossils]

Nope, just a nodule

 

[rock]

Ok thanks. I just dont find fossils much here.