An Art Deco amethyst, onyx and diamond pendant, 1920s, the pendant composed of a polished amethyst

An Art Deco amethyst, onyx and diamond pendant, 1920s, the pendant composed of a polished amethyst within an intricate platinum openwork mount, set with rose-cut diamonds calibré-cut onyx and two pearls, suspended from a necklace composed of navette-shaped and spectacle-set links set with circular-cut diamonds, necklace length 57cm, pendant length 7.5cm