The oval links and backplate of the pendant look like horn. All of those black materials used in the 19th Century and through the early years of the 20th Century, though, can be difficult to identify when you have them in hand, let alone through photos. If you can get some strong light on those parts and look for brown tinges, translucence, grain/texture and type/strength of luster it would help. Here are some reasons why these can be so confusing:
Gutta Percha and Vulcanite brown over time, are usually matte rather than glossy and are usually molded, so you can sometimes find mold lines with a loupe. Pressed horn, however, is also usually molded and dark like Gutta Percha and Vulcanite. Vulcanite, by the way, can be a variety of colors, and though Vulcanite was rarely used to make jewelry, rarely is not never. Jet is carved and usually, but not always, glossy. Bog Oak is also carved, can be glossy and often has a woody texture. Tortoise usually, but not always, has translucence and is carved and mottled with lighter and darker areas, but not always. The flowerpot and black links with the X's could be any of these. There are even more possibilities such as French Jet, a fancy name for black glass, dyed Onyx and even Celluloid.
I do think it is Victorian from the 1850 - 1900 period, probably 1860 - 1880. I would also guess that the oval chain links are horn, the black links Jet due to the sleekness and luster, and the pendant Horn with a molded Vulcanite flowerpot. Possibly French, too. A beauty, Mary Jane.
