These pendants are amulet cases. They are made from various materials, but essentially (originally) metal, transposed into minerals and glass. They are also called "charm cases."

The metal versions were sometimes boxes that opened, allowing the owner to place objects inside, including religious or magical writing. Some are hollow, but do not open. These may have small holes—the idea being that they could be dunk into the River Ganges (in India) or any holy river, and thus become "charged."

The shape became so popular, that these were rendered in stone—often agate and carnelian. Whereupon the shape itself was considered amuletic. And eventually they were made in glass, imitating the stone versions. Some of these were mass-produced in Czechoslovakia, in various colors, and were molded.

The grand proportion of agate/carnelian versions (such as yours) were mostly made in India. Yours are probably antique, but perhaps not ancient.

Good luck! Jamey