Hammer stone or just a rock?

[Syrix]

This is a central Missouri field find, in a location that I have found several tools and enough debitage to fill a truck! I feel like I finally have a good handle on identifying a point, but have always struggled with what is a hammer stone and what is just a round rock. So I need some expert opinions on exactly what I have or haven’t found. Thoughts?

[SurfaceHunter]

Looks like a flint nodule to me they did use them sometimes but you’re nicks on that one look fresh to me so I’m thinking rock

[Kaleb]

It almost looks like a small pecked in depression in the 4th picture but I doubt out because nodules like that don't usually have a verry thick crust. Still cool though, I've got a pile of stuff like that in case i ever get into knapping

[Kaleb]

This might not be much help cause I'm in Utah but this is what flint/chert hammerstones look like in my area

[Hoss]

I think it is a sedimentary rock that was struck ans chipped by a farm implement.