This is a gorgeous antique carnelian drop choker made by the venerable Canadian silversmith and jeweller Birks - Birks is considered to be the Tiffany of Canada.  This choker is made of sterling silver links that are set with marcasites.  The necklace measures 15 1/2” laid out straight with a 2 1/4” drop.  My mannequin has a narrow neck, but this will fit like a choker.  I believe that this choker would date to the 1910s, possibly early 1920s.  This antique carnelian drop choker feature features fine workmanship as one would expect from Birks - lovely piece of jewellery!