I went to the next step for ID-ing these. One bead was split apart. Ignore the red splotches - that was the paint coming off the hacksaw blade. After sawing a notch, I split the bead with a chisel. The internal structure was fibrous.

Next I burned the edge in a torch flame. The material did not catch fire, but beaded up and charred with a distinct "burning hair" smell. So, I think the beads are made from some sort of horn. But since I've never torched bamboo or ivory nut, I can't be 100% sure.

The density of the material is similar to amber - probably close to, or less than, 1 g/cc.

Any other thoughts would be appreciated, and for Hans - I'll send full size pictures if you want them for your broken beads photo album.