crabstone

Etymology
From.

Noun

 * 1) A calcareous concretion found in the stomach of crabs and other crustaceans.
 * 2) * 1999, Mike Mitchell, translating, Simplicissimus, IV.8, Dedalus 2016, p. 303:
 * [F]rom cadmium, gravel, crab-stones, emery and talc I prepared a powder for whitening teeth, and from lye, copper, sal ammoniac and camphor a blue tincture for scurvy, stomatitis, toothache and sore eyes.