I have actually viewed and photographed this stone under a microscope. Seen here are three views of a sange Maryam bead (or beads--I had these shot a while ago).

I have been inclined to suspect that the mollusk typically found in this material is a univalve (a snail). Note the left part of the image where a spiral can be seen, that is easier to explain as part of a snail shell than a clam (or the like--a bivalve). Nevertheless, Peter Francis asseted that the "shells" were from a different phylum all together....

Regarding the size of the radulae ot teeth, they are admittedly small (whatever they are), but since we're dealing with fossil creatures that died millions of years ago, a comparison to the radula of a modern snail might not provide an apt comparison. In any event, I'm not married to the idea, but I would enjoy seeing/reading anything that scientifically identifies this material and its inclusions. I hit upon the idea of radulae because, apart from the external shell, these are the only hard body parts a snail is likely to have. A clam, of course, does not use a radula for tearing food. You may be totally correct in your alternate identification of the smaller inclusions, or in general.

Cheers, Jamey