This stone came to me, sealed in urushi and handwritten in kanji "Naurtaki" on the side. A modern mined stone, maybe from the post-war 50s, it is a utility size that was likely set for small pairing knives or such. I use it as a hand-held kitchen knife stone on carbon but especially handy for stainless or carbon steel. For honing, I use simple back and forth strokes.
Hardness grading is Mohs 3-  so it matches well with a wide variety of steels.