This is an early Onyx Mourning brooch made with Pinchback . It is 2 3/4" long with a 'T' bar and 'C' clasp and has a flower and leaf embellishment. It is 9.1 grams and in very good condition for an item over 100 years old.
I do see a spot of solder and some loss of finish. But I think it is worth it to preserve and move on.
Early Onyx Mourning Brooch