Rivets, buttons, snaps??

[roccus]

I dug these out of the ground next to an old 1800's wool mill. I am not sure if they are copper or maybe bronze and not sure if they go back to the 1800's. I put a penny next to them so size could be gauged....

Front side...

Back side...

 

[roccus]

Must be pretty rare then.... seems nobody here knows... thanks all anyway