Ive ground down a stone before and it ended up in some pretty fine dust. I used a cheap tile cutter with a diamond blade and just ran the stone through it one line at a time. The catch underneath the tile cutter will trap most of the cut stone in a water slurry. Pour it off, dry it, and it crumbles to dust. I did this a year ago but never got around to testing it in a glaze. Im sure theres possibly a level of metal "contaminating" the dust just from wear and tear on the blade. Either way it beat pounding with a hammer and dealing with a container bouncing around as you hit it.
Oh and because you have to remove the guard on the blade you are bound to get a little wet so wear a face mask.