Know about the Grindstone?

We have a heavy millstone in our collection with a tag from an anonymous donor.

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We were contacted by the Cleveland Museum of Natural History and Joe Hannibal of the Cleveland Museum of Natural History stopped by and assessed our mill stone.  Our mill stone is French buhr, a type of chert (“flint”) found in the Paris Basin (a geological area around Paris).  The stone has fossil charophytes in it that show it is the French stone.  Such stone was widely used in the United States in the 1800s for millstones.  A great amount was imported from France.

Does anyone know anything about this stone?