I have such a stone ~2x8",mounted on a wood base with a wood cover. I think it came from Woodcraft Supply 15 yrs ago. I use it to do a final edge finish on my hardwood chisels (with very thin honing oil).

Anyone have any idea what the effective "grit" size might be on this? It is very fine relative to other hard Arkansas stones I have, and has the sense of being "harder". It is uniformly almost completely black.

Just curious and figured one of you has had their hands and maybe blades on such a stone.

Thanks in advance.