I did an image search and found some sites which discuss this specific jewel. I also found similar pieces of jewelry, all dating back to the late 1600s to late 1700s. The general consensus from the sites I visited was that this piece was originally a brooch, with the part below the cameo and the loop on top added much later to make the brooch into a pendant for a necklace. It seems that these types of cameos came from France or Itay, which got me thinking, and now I wonder if it was a personal gift from the Empress Eugenie to Victoria. Those two were very close and they did exchange presents. I suppose we'll never know for sure!