This pin is really old but either it is not antique or the clasp has been replaced. It has a bar and safety clasp now.
The pin is a hexagon and features a dried flower pressed between an opaque pink back and clear glass front. It is framed in silver or nickle (my guess is nickle silver) that turns protectively over the edge of the glass both front and back. It is 1¼ inch across and ¼ inch thick. Really a unique piece for collector's of vintage/antique jewelry.