Vintage delicate necklace with natural pearls that look like Black Tahitian

Delicate style necklace with natural peacock color pearls. They are of high luster and dark blue / purple color, and look like natural Tahitian black pearls. Can't say for sure if these are true Tahitian, or cultured. But they don't look like typical freshwater r/ iver pearls. 17" around the neck, with 2" extension. The free hanging part is 2" long. In excellent condition.