The first thing is to get out of the "certified organic" mindset. Per Howard's and Rodale's work, as well as a lot of field researchers over the years, the use of rock dust is valuable for micronutrients and trace minerals and therefore part of organic methods. Whether it is "certified organic" is another story. Certification is all about marketing and co-optation of a valuable paradigm by government and its lackeys. I use 5# of glacial till dust in each 80# batch of fertilizer I make up. If you add granite dust, there is also a little bit of potassium in it, but it is slow-acting. However, slow-acting compounds are another consideration, as the weak acids in the soil will break them down over time, thus providing a reservoir of fertilization.