Help to I.D. hone

I picked this up at a garage sale today for $4. I have no idea what it is but I was just curious and for $4 you cant really loose.
I lapped it and cleaned up the edges. I then gave a completely blunt blade 15 laps over it with almost no effect on the blade, but thats all I've done with it so far.
It seems quite hard and fine and if you look at it on the right angle you can see fine sparkles in the surface.
It also did seem to develop a light grey slurry when lapping. Its 2" wide by 1" thick.
The pics below are before and after lapping
Thanks Grant

Nice snag, $4, wow. Looking at the color, and reading about the light gray slurry you got, maybe it's an old Thuringian? Maybe one that was originally 7 X 2", and got broken off or dropped? Or maybe a dark blue Escher, some of them came in bigger sizes than other Thuringians, which are often more like 5 x 1". My Eschers/Thuringians aren't as thick as what you have pictured, though, they're more like 3/4" thick.

I've never seen a Thurry that thick, but that certainly doesn't say much because I've not seen all that many. Also, pics can be decieving, but I think that looks too coarse for a thurry in the second pic.

I've had the new MST Thurry, and a vintage thurry, and neither one has sparkles in it, though the color is very similar.


I used a microscope at 100x to evaluate the scratch pattern on mine.