Yesterday I dug the back of a scovill button that looks almost the same. It is the back to a 2 piece button. The face was evidently broken out a long time ago. It's fairly common to find them like that in civil war camps. It does , like N.T. said, look like it is probably an EVANS back. Evan's took over Robinsons in 1847 so that back could date from then to just after the civil war