I don't know all that much about them, they are a pre-courser bead to some of my Kiffa beads, the Mauritanian Nomad Women that made the original Kiffa beads have an almost identical looking bead as the one I posted, I assume they are from that time period. I have several in various states of preservation, from pristine to badly worn. The sizes are all pretty small, around 8mm x 9mm.
The picture shows the comparison between the Kiffa and the Islamic.