Quote:
Arkansas Novaculite stones are classified by specific gravity and not the size of the grain. The grain of the silica crystals that form Novaculite are essentially the same size, 3-5 microns, whether the stone is classified as Soft Arkansas or True Hard Arkansas. Using Specific Gravity Testing, Dan's Whetstone Company measures the density of their stones, that is the compactness of the grains bonded together. Therefore the harder stones would then have more grains than the softer stones. Since the grit size of Arkansas Novaculite does not widely vary, it is difficult to compare it with the grit sizes of man-made stones. Grit measurement standards for traditional man-made stones vary internationally. By U.S. grit standards, genuine Novaculite most closely relates to the 600-1200 grit size.
I'm sure you've seen it mentioned before, but these aren't slurry producing stones so the grit size doesn't have much bearing on the performance of the stone.