Nice coticule.

I would need more information on the large light gray stone. It's impossible to tell from the pictures whether it's completely smooth and non-porous like the coticule, or, is it a porous stone? Putting water on the stone won't always prove porosity since the stone could have been used with oil or lather.

An extreme close-up would help.

I have a stone identical in color somewhere. However, it's a very fine grained sandstone, it's porous and soft. It's useless IMO for razors since it's a very grainy stone. It freely releases the fine grit which you would think would be a good thing (slurry); however, the grit even though fine for a sandstone, is still large in razor terms.

Chris L