I don't know what it is but I suspect it is decorative as a opposed to military although it contains military or patriotic elements.
The background has an eagle clutching a flag bearing stars with a spear tip. The man in the front has a hair style and hat of the late 1700s French style, large hat with feather and a trimed moustache and hair on the lower lip, like a "musketeer".
Could be a broach or hat decoration, probably a ladies decoration.
My first thoughtwas the back piece was a scrap or shard of something but your pictures show clearly that it is art of the whole object.
A good find what ever it is. Is it plated or solid metal?
HH
1859