This large-size (grade #35) bench stone is by definition a tomae strata layer. Tomae tend to be medium hard Mohs 3, often pale green that can appear yellowish when wet.,
 
Sumi-no-gashi translates as the appearance of ink floating on the surface of water. They can be colorful and are not specific to any one particular strata. often of alternate minerals types are grouped with the Uchigumori type. This stone #2149 represents the "Hazuya" type of uchigumori. I would recommend that this is a knife stone, it will handle a wide host of steels. I have honed straight razors on #2149 with success but it feels awkward honing a razon on such a large stone.
 
The back and front are perfectly flat and the sides and ends have been formed with a hand saw called a Tsuru-noko (2 man push-pull saw) that leaves a diagonal scratch pattern on the stones sides and ends. All of the Hoard Stone collection were mined in the Meiji Period, and the sides and ends were at that time all hand sawn.
 
Grade #35   204-73-28
1120 grans = 37.8 ounces
Mohs 3