It looks like it could be a fossil, tho I don't know my geology well enough to begin to speculate as to what kind of fossil it would be, if it indeed could be. It looks like it could be a rock, chalcedony in-filled with limestone maybe, however strange a shape it's taken.
I've done my best to set it aside, trying to wait out my curiosity while it sits with the other chunks of chalcedony, but I can't stop looking at it.
Please help!
K