#775 Uchigumori is likely from either the Narutaki or from the Nakayama mine (they are less than 1/2 mile from each other). I suggest these mines because I have hiked and collected samples from each of those two mines and their namazu is often a form of streaks, instead of patches like from the Ohira. The last photo as an example of streaks is of a 15.5 pound piece of uchigumori I picked off the ground, with permission of Mr. Akira Kato in March 2017.
 
#775 uchigumori weighs 1121g/2.47lbs. it is 204 x 77 x 29mm. The main lines of visible non-toxic namazu  are on the back side, or the interior where it cannot yet be seen.
This stone is the Hazuya form of uchigumori from the Tenjyou suita strata, the second shallowest strata of the recognized as 10 to 12 specific layers in the Honkuchi stratification model. Its Mohs rating is 3-. Cutting speed on steels of course will vary from one steel-stone combination or another, but I have not problem finding shave ready edges off this stone which is my benchmark.
A tested large tomonagura slurry stone will be included.