18” long sterling necklace 3 stunning charms! 🌸

Gorgeous and weighty 18” long serpentine sterling Mexico chain supports 3 gorgeous charms. One is onyx pin/pendant. Approx 2.75” long x 1.5” wide. Stamped Sterling and I think 819. The next charm is slightly hammered 1.5” x 1.5” with faint scrolled initials on front that says, “SOS”. Stamped Mexico and 925. The third charm is 2.75” long x 2” wide. Also stamped Mexico and 925. I’m not sure what the stone is. All are tarnished. I like the look!