Mikawa Shiro Nagura Yae-Botan 5.4oz. (157g) Japanese Natural Sharpening Stone
Approximately 40mmx45mmx40mm
It is pretty nice shape, color, and lines
Koma, Mejiro, and Tenjyo are fine grit layers of Mikawa Shiro Nagura.
Mejiro is one lower grit or little more aggressive stone, but in Mikawa Shiro Nagura, the grit of Mejiro is very useful.
According to Dr. Kuniichi Tawara who is a Metallurgy doctor, and very famous Japanese sword researcher, Koma molecule is 10 to 20 microns.
It should be good for two processes before starting the fine grit sharpening.
For razor sharpening, it is used two processes before sharpening by fine grit whetstone like Nakayama, Ozuku, Wakasa, etc.