Stamped "STERLING" I dont see any other makers mark on the piece Looks to be antique, before WWII, and maybe of mexican origins/style.
Dimensions
looks to be 15.5 to 16 inches in length, about 1 inch in top to bottom. 15 Black onyx stones.
Acquired From:
Auction House
A Silver & Onyx Fringe Necklace, in the Mexican style, the 15 black stones within beading surrounds with silver backing, clasp stamped "STERLING", 15.5 to 16" in length, about 1 inch in top to bottom. N.B: If the stone is not onyx it could be Obsidian which is natural volcanic glass.