The second pictures shows some small flake like cracks that is more novaculite like than thuri.I have a similar stone which I thought might be a Thuri. But until recently I had never used one, and side by side they were certainly different.
Smelt similar, lapped similarly (the Thuri slurry* was a bit darker), but the stone below was harder and coarser.
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* There's a good tongue-twister in here... She sells slurried Thuris on the sea shore.