Professional grade Nakayama Aisa that would have been used in an industrial workshop for honing oversized blades like the 80mm Chiyozuru kanna blade in the photo.
 
A highly productive stone for large blades this size stone would have been used by either a professional knife sharpener or a mia-daiku master carpenter for sharpening extremely wide kanna blades or unusual chisels.
 
I can not honestly say from which mine this suita came, but it has every indication that is was dug in the lower portion of the valley at Narutaki or Nakayama. I have one stone (karasu #2200) of the same size that I dug myself with the permission of the Nakayama mines owner at the Nakayama Spring tunnel entrance.