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Use the given link, there are also the black mottled ones shown...

Check Peters post here:

http://straightrazorpalace.com/hones/112608-late-thuringian-escher-stones.html

https://farm6.staticflickr.com/5704/20586648612_3d35e0b636_c_d.jpg

Looks like a Schwedenstein, they also appeared in these boxes or on small paddle strops and boxes...i will add some pics later

Is there a visible pattern? Or is yours tending towards black, in one...