This is a keeper, an Art Nouveau - Arts and Crafts transition brass sash brooch. The cobalt and light blue stone or porcelain is unknown to me. It is set inside a fleur de lys bezel. The outline of the pin looks like a shield. Has an old C clasp.
There are no makers marks on the brooch.
Almost 2 ½" wide x 2 ¼" tall.
There is some oxidation on the pin. You can polish it or not.