When the popularity of black mourning jewelry exploded in the mid 1800s, jewelers used all kinds of materials (Whitby jet, French jet, vulcanite, enamel, etc) to create jewelry with the uniformly dark appearance that social custom dictated. Enter gutta percha, a cousin of rubber made from the resin extracted from tropical trees with all the right optical properties: dark color, low luster. This deep brownish-black chain is made of molded gutta percha with graduated (and variously shaped) links. It's a nice long length - 24". Despite the popularity of gutta percha jewelry in the mid 19th century, pieces made from this material are somewhat rare owing to the fact that it was heavily used to make underwater telegraph cables. The supply was exhausted in the late Victorian period.
Gutta percha, lacquered metal clasp
24" total length, largest link 1" x 1 1/8", smallest link 5/8" x 1/2"