Here's a really zoomed in pic of a sample piece they sent me. The bigger white markings in the middle of the pic are the stab marks made with a sharp knife. (Stabbing pretty hard). The smaller white marks to the upper right of that cluster is the dust. To give scale, the knife marks are each about the diameter of a needle. In person the dust particles are barely visible.

No idea if this helps or not, but just thought I'd put it out there.