Thread: Help id this natural hone!

Well 25 years ago, at a local auction i purchase 3 boxes of woodworking stuff, mostly old planes and chisels,
a few sharpening stones and other stuff as well, anyway this huge stone was in there and its been in my basement all this time, so while doing a little cleaning today there it was, so i decided to start lapping the hone its 13 x2 x1, 1 pic is dry
2nd pic is water 3rd pic is with slurry the colors from the pic are very close, after a little lapping the surface is very smooth
what do you expert think??? notice the two gren specks in the second pic?