Mikawa Shiro Nagura 12oz. (336g) Japanese Natural Sharpening Stone
I am not sure which layer of Mikawa shiro nagura, but it looks medium-high to lower side of fine grit. It does not look finest class in Mikawa shiro nagura.
It raises great amount of dark gray or light black color slurry.
(Scale; 1 to 10, 1-3 is very soft muddy rough grit whetstone 3-6 is soft medium grit whetstone, 6-8 is hard medium grit whetstone; 8-10 is fine grit whetstone)
It makes my blue II steel kasumi blade knife Hagane became bright silver color finish. Jigae became frosted silver color finish.
(Scale; 1 to 10, 1-3 give deep scratch marks to the steel, 3-5 is delete the 1-3 scratches, 5-8 makes the steel cloudy, 8-10 makes the steel semi-mirror finish or mirror finish)
According to Dr. Kuniichi Tawara who is a Metallurgy doctor, and very famous Japanese sword researcher, Koma molecule is 10 to 20 micron.
It might be like Tenjyo and Mejiro and Koma class grit.
It should be a good sharpening stone right before starting the fine grit sharpening.