Buhrstone

• (n.) A cellular, flinty rock, used for mill stones.
Found on http://thinkexist.com/dictionary/meaning/buhrstone/

Buhrstone

Buhr'stone` noun [ Middle English bur a whetstone for scythes.] (Min.) A cellular, flinty rock, used for mill stones. [ Written also burrstone .]
Found on http://www.encyclo.co.uk/webster/B/110

Buhrstone

Buhrstone or burestone is a name given to certain siliceous or siliceo-calcareous stones, whose dressed surfaces present a burr or keen-cutting texture, whence they were much used for millstones. The most esteemed varieties were obtained from the upper fresh-water beds of the Paris basin, and from the Eocene strata of South America.
Found on http://www.probertencyclopaedia.com/browse/HB.HTM
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