Seeing the way they are arranged on foxtail chain and that clasp-
I have very similar beads necklaces.
If you look at the end of each bead around the hole you will most likely notice that there the blotches are not evident, because they are dense lampworked glass created with a minimum of bubbles to resemble stone, perhaps jasper or limestone, the whole necklace is heavy also because of the chain.
At the Istanbul conf. in my talk about "realistic replicas and fascinating fakes" I showed examples with extremely similar beads with the same clasp almost certainly made and threaded in Czecho.
Unfortunately my presentation didnt make it into the printed volume.

Can you show an image of the end around the hole of any of the beads?

If they were stone its likely the holes would have been smaller if anything and the markings would continue all over.