I would say it is some sort of brooch. The tramlines on the back remind me of how the fastners were attached on late 19th century/early 2oth century pewter or zinc items. This is just a guess based on the limited information you have given :-).
I believe it is an antique clock pendulum-weight, whose attachment-loops are broken off the back's ends. (Its size is consistent with that ID.) The groove in the middle of its back is where the long iron rod which connected it to the clock went. There is a very-nearly-identical match in the photos below.
Hello Folsom1. Welcome to Tnet. Whether a brooch or a clock pendulum, I LIKE IT. I gotta say that you should go with clock pendulum because the cool-factor somehow seems higher, nice dig. HH C9