I believe most people don't really care what the actual grit is of a natural stone, but how it "behaves". Does it behave and cut like a 4000 grit, or does it behave and cut like a 12000 grit? Grit ratings are just a convenient overall rating system. If you have a very fine natural stone and it cuts like a 12K synthetic, why not call it or liken it to a 12K? When all things are considered, grit is just a comparison system. Does .5 micron (or grit) cut better or worse than .5 micron CrOx or , FeOx or CBN? They are all the same micron rating. But because of the shape and hardness of the compound they cut drastically different and produce vastly differing edges. Don't get hung up on grit ratings. Look for a fine stone, be it natural or synthetic that will behave like a 12K and you will be happy. In my opinion, anything above the 12K-15K grit ratings are not really grits as much as polishing abrasives. You will get a different finish off of a 1K stone than you will get off of 1K grit AlOx or SiC sandpaper, but they are all the same grit. Remember we are here to help, not condescend or be stone/hone snobs. If you scraped the label off of a vintage Escher, would it polish better than a no name Thuringian? Other than collector value, they are the same. I would rather have a cheap Chinese 12K or no name Thuri that cut and polished well than an overpriced Escher because it has a label on it. Rick