Vintage Rough Grit Japanese Natural Sharpening Stone 4lb. 11.6oz. (2141g)
220mmX75-78mmX50-54mm
Probably, it might be Omura rough stone.
It is not easy to find Natural Japanese stone in Hawaii, but I found it here in Hawaii.
Hawaii has a long immigrant history from Japan (I guess it has been over 160 years), so Carpenter, barber, cook, fish cutter, butcher, etc. needed good sharpening stones, especially carpenter and barber needed high-quality fine grit stones in old days (until King synthetic red color sharpening stone came up on the market in 1960s, Aoto is the main medium to medium high grit sharpening stone).
Hardness-------------8.6
It raises very good amount of slurry quickly.
(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)
Particle Size----------5.6
It makes my Swedish pure carbon steel / soft iron blade knife;
Jigane became deep scratches on the sharpening surface, and Hagane became bright silver color with strong scratches, however those scratches are not super deep scratches.
(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)
Natural whetstone has wider capacity than artificial whetstone, and actually, we do not know until sharpen blade on the hone for a while. Because artificial whetstone molecules do not break down to smaller sizes, but Natural whetstone molecules are possible to break down to smaller sizes, and those molecules are mixed with sharpened steel molecules, and make Jigane as suitable Jigane color, and Hagane as suitable Hagane color. It is natural mystics.