You should hold on to it and try and find out more. They appear to be very rare. I collect miniatures (hobby) and I have only seen one other which was silver and black onyx. One of my colleagues believe the little containers were handmade for the sole purpose of concealment, to hold opium for a the wealthy or doctor. Another colleague believes that it was akin to the ring that held a poison like hemlock. All good theories, but with such a small container the majority of us think it was a Talisman. The miniatures can sell anywhere from a couple hundred dollars to a couple of thousand. I hope the meaning is not lost to history. We may find more in England's journals. Good find.