The crystal explanation makes sense to me. Here's a place that sells CR203 in average grit size of 50 MICRONS. I ordered a small packet just to see how different that would be from the reported .5 micron we all know and love.

50 micron Chrome Ox

Under "About our Pigments" area it states: "All of our pigments are ground to 50 microns for ease of mixing." I confirmed this in a prompt email reply from the company when I asked for the MSDS sheet since it was not one of the ones listed on the site. They also reiterated that the Viridian (Chromium Oxide CR203) averages 50 microns in particle size.

Chris L