buhrstone
buhr.stone \'b*r-.sto-n\ n [prob. fr. burr + stone] 1: a siliceous rock used for millstones 2: a millstone cut from buhrstone
buhr.stone \'b*r-.sto-n\ n [prob. fr. burr + stone] 1: a siliceous rock used for millstones 2: a millstone cut from buhrstone