This is a lovely vintage Art Deco festoon necklace made up of numerous small faceted amethyst glass stones in open back settings. It is a simple and elegant design. The necklace is suspended from a delicate chain and fastens with an old style spring ring catch. The silver colored metal is most likely silver plate over brass.
The necklace measures 15 inches long. If you wanted more of a drop, it could easily accommodate a necklace extender. I use these myself as many of the necklaces from this era are on the small side. It is in very nice condition with some light surface wear, particularly to the catch.