The nomadic Tuareg of west Africa are considered master craftsmen, and rings like this were believed to have protective powers. We call it the rattle ring, as when you shake it, there is something that rattles inside of it.
They would carry many items of jewelry for protection and guidance. Made from tribal silver. This particular ring amulet, was believed to give its wearer protection.
Diameter: 1 3/8". Top of ring is 1/2:, and size is 7 1/2.