These bar pins were hugely popular for quite a long time so sometimes it is hard to pinpoint. It is most likely late Victorian but could be as late as the onset of Deco. In other words, 1900-1920s.
No it is not marked and it is much earlier as the Deco Period began at the very end of the Victorian Era, which was preceded for a brief time by the Art Nouveau Era(my favorite era). It is Late 1800's to Early 1900's which actually puts it in the Edwardian Era, but that lasted for only about 6 years, so is not often referred to in generalizing. I hope this helps. It's a stunning piece that I have worn as a pendant on occasion.
Thank you so much for your question and good luck bidding!