From the photo the bead looks like it's made of glass! But holding it in your hands you say it could be stone, unfortunately I have only the picture to go by. If it is stone then I would assume the same process they used to make dZi beads could have been used here also???
I would take a strong magnifier and look for tiny air bubbles, at least this way you could rule out glass for sure? My hunch is that it's old and glass and the age makes it look like stone, maybe someone else could shed a brighter light on this!
Good luck, Thomas