Photo is current.Ozuku stones are famous in the very small world of Japanese natural stone sharpening. They were used to put the final edge and polish on swords and other knives. They have been mined in Kyoto for hundreds of years. In the 1970s the mines were closed since the population of Kyoto started to encroach on the mountains that surround the city which has made the stones very hard to come by. This koppa which translates to "small" is sold at a fraction of the full size stone cost.
The estimated grit range of this stone is about #15000 and that is a guess since natural stones are not completely consistent with particle size. There is one stamp on the top of the stone. It weighs 452g.