This cylindrical key is a "Bramah" type, patented in the 1780s, and it is hidden inside a silky-smooth, HEAVY gold cross. The owner would have used it to unlock her jewelry box and simultaneously hide the key on her body. More about Joseph Bramah, the inventor of this technology (and one of the thought leaders of the industrial revolution): he also patented an improved toilet valve, the hydraulic pump, a type of fountain pen, and a fire engine.