Shobu mine has various stones with many colors: red, yellow, green, gray, etc. The ones we are getting currently are green/grey and hard. They are fairly high grit finishing stones. The one that we have in stock is 1lb 6oz and measures 8" x 2" x 1".
The Shobu stone is an excellent mid-range polisher, or finishing stone for those who want a great follow-up for a 2k or 4k stone. We estimate this stone to be in the 8,000 grit range. When followed by an Asagi stone, it can produce an edge that will easily be shave-ready with a handful of strops on fine compound. The smooth feel aids in polishing the edge, which this stone will produce a semi-mirror finish. Like most naturals, the finish is a bright matte that is nice and uniform.
It is fairly hard like most natural stones, but with a soft feel and is rather forgiving as far as naturals go. It will produce a fair amount of mud with a nagura, but isn't what you'd classify as a "muddy" stone. Like most naturals it is very slow wearing and should last you for years and years. These stones really shine on carbon steels like Hitachi White and Blue, or 52100, and also work great on stainless as well.
This is my 5th natural stone,and I must say it is now an indispensable part of my natural stone sharpening routine.
I normally establish my bevel with Shapton stones,then move on to the Shobu. You can go from a 2k or 4k edge staight to the Shobu with excellent results. I work up a little mud with either another natural stone,or a piece of Arkansas stone as a nagura. Or you can just use a nagura! The mud readily forms on the stone,and the stone has a "silky" feel. The resulting edge is in the 8,000+ grit range,and has a nice bright smooth finish. You can stop here for an edge that still has some teeth,or move on a higher stone,which is what I do.
The stone I use after is the Asagi Koppa,and if you are using carbon steel... this combo is deadly! The Shobu and Asagi are an excellent pair,and also give you a long lasting edge. The Shobu is great to use an a nagura on the Asagi,due to the fine mud and its nature to break down even finer.
It is almost a muddy stone,but not quite,and is still very hard. Splash and go!