Perhaps my arkie isn't as hard as your new ones. I did do a specific gravity calculation on the rock and it worked out at 2.53, so it might be on the cusp of been 1 or the other in terms of hardness.

This is an image taken today of it.

Bering in mind the only finishing it has received in this image is from hones, It was a raw 400 grit finish before I started to play.



I don't think it's finished in terms of glazing, But it's certainly taken something from those hones.

Just a note of caution - if you do lap an arkie try to use lapidary grit for the coarser lapping and wet'n'dry sandpaper for higher grit lapping - arkansas stones and hard novaculites of other types have the sad potential to ruin a diamond lapping plate by removing the diamonds altogether or by smoothing them so that a 325 plate performs as slowly as a 600 grit equivalent.
I clocked onto this when I first posted the images of the arkie to try identify it. I think it was you actually that told me to avoid using the DTM on the stone, Ever since I've used wet and dry. The DTM400 is for the softer stones. I was actually looking into a lapping plate, There are a few available, but I think I'm going to hold out and see if I can get a badly listed ebay one. They come up from time to time, and looking for metal chess board sometimes throws up some lovely randomness!