Arkansas oilstones

Natural novaculite, no grit number

Arkansas stones have no grit number at all. They are graded by density and finish. The microns here are not a maker figure: they come from an independent microscope study comparing scratch patterns against micron-rated film. So they are ranges, they describe the effective cutting size rather than a nominal grain, and specimen variation keeps them an estimate.

Each grade below shows its size in microns, its spread (the published distribution, where a maker or standard gives one; most makers publish none), and where that size lands on the reference scale, a shared yardstick for reading grit numbers across makers.

Particle sizemicrons, log

1053

coarserfiner

inkmeasured or standardmaker figureour estimate

shapeknown distributionpoint, spread unknown

Soft ArkansasOur estimate

12 µm

Range 10 to 14 µm. Effective ~12 µm (about 1200 CAMI by the scratch study).

spread 10 to 14 µm · reference scale about #950

Hard Arkansas (white)Our estimate

10.5 µm

Range 9 to 12 µm. Effective ~10-11 µm (about 1500 CAMI by the scratch study).

spread 9 to 12 µm · reference scale about #1100

Hard Black ArkansasOur estimate

7 µm

Range 6 to 8 µm. Effective ~7-7.5 µm (about 2300-2500 CAMI).

spread 6 to 8 µm · reference scale about #1850

Translucent ArkansasOur estimate

6 µm

Range 5 to 7 µm. Effective ~5.5-6 µm (about 3500-4000 CAMI by the scratch study).

spread 5 to 7 µm · reference scale about #2200

Surgical Black ArkansasOur estimate

4.5 µm

Range 3 to 6 µm. C-estimated, weakest sourcing here.

spread 3 to 6 µm · reference scale about #2750