Thick parallelogram of Honyama suita.
This flattened and ready-to-use piece of light colored suita has amazing cutting powers when put up against boutique steels such as hand-forged Japanese blades, Swedish steels, vintage antique steel and wrought iron, and others. It is not particularly effective with stainless steel.
 
It has a living edge kawa volcanic skin on all four sides and the back has been flattened at the mine site with a chisel. The shape of the stone indicates it was dug from a shelf in a nook. The toishi is too large to fit into a commercial stone holder but it will easily arrange on a bench. The stone weighs about 7 lbs. / 3125 grams. 310 long x 140 wide x 30 mm thick. Relatively hard at Mohs 3. I bought this and a couple of other stones in a rural town in Ishikawa-ken prefecture about 25 or 30 years ago.
 
I can not honestly say from which mine this suita came, but the stone has every indication that is was dug in the upper portion of the Umegahata upper valley in or around Oozuku or Ozaki.