The stuff acted weird! All of the particles fell out of suspension very quickly, which would normally indicate that they are large. In this case they're not so I just went ahead with the process.
There was a lot of slop left over, though. If this test works, I'll go ahead and grind this down to make more one particles.
At the end of the day I really wanted to feel the grit of these particles under the muller. Even though they seemed large, they felt fine to my hand. Tomorrow will be the real test when I add this powder to an ink base and test it on paper.
At this point I got on the internet to see what I could find out about soapstone. It's talc, which explains the extreme softness and strange slipperiness. I also learned that it's used in the recycling process to release ink particles from paper pulp. This might be a bad behavior if my goal is to get them to stick to the paper surface. I'll try it and see!