I don't like having to disagree with Iron Patch, whom I respect. But using T-Net's option to super-enlarge the photos, it sure looks like a 2-piece button... having a silverplated/nickel-plated thin stamped sheetbrass brass front crimped over an iron back. In the super-enlarged backview photo, you can see the crimped brass rim around the edge of the back. The crimped rim shows some green brass patina in a couple of places.
If it is indeed a 2-piece stamped-sheetbrass/ironback button, it can date anytime from the late-1820s onward through the 1900s. If its sheetbrass front is nickel-plated instead of silverplated, it would date from the 1870s onward.
The multi-multi concentric circles design on its front means it is a Civilian-usage button, not a Military one.
Due to the backview photo being shot almost straight-downward on the button, I can't be sure, but I seem to see an iron stud projecting from the center of the back. If that is correct, it is an Overalls rivet-button, dating from approximately the 1880s through the present.