These stones from Japan are not JNAT, but are synthetic whetstones very close to natural stones. A craft man named Mr. Morihei devoted all his energy to developing this new type of whetstone for several decades. He combined both elements at a specific mixing ratio on selecting high-quality raw materials of both natural and synthetic stones. Finally, he succeeded in creating this newest semi-natural/synthetic whetstone.
Every MORIHEI stone involving grit of 500, 1000, 4000, 6000, 8000, and 12000 are fired at low temperature, and the temperature burning each stone grit is slightly different but not disclosed. To the best of our knowledge, it seems the whetstones are manufactured not by the magnesia method but by either vitrifying or mostly resinous means.
The official name of this series is MORIHEI Hishiboshi (MORIHEI Hi).
I have found these new stones to be something unique.