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The small stone looks as much like a coticule as the large one does.

I would try lapping it before bothering trying to de-grease it. Coticules don't seem to soak oil very far in anyway, so you...

I agree that it's probably an oiled two-sided coticule, with the two sides glued together. If you produce a slurry on the lighter side, and it is a coticule, then the slurry will be milky white. If...