I inquired about some natural Japanese waterstones....

These are not truely rated by our grit system and in some ways they are nice to look at simply by shape, size and color. The Japanese seem to describe them as "hard" or "soft". But they also say that they start in the 20,000 grit range. So; you have to go a bit on instinct and advice when looking at them. I was after a next step beyond my yellow couticle. Why, you ask?....
Not sure I have a good answer...to some degree, it is the appeal of using natural stones. Japanese culture also has appeal. architecture, tradition, martial arts, weapons...so why not rocks?

Anyway I have a couple on the way that I hope are of differing grits. I will share my reactions once they arrive.