Also buhr-, burrh-, bur-. [f. BURR sb.5 + STONE.] A siliceous rock of coarse cellular texture, found chiefly in France and N. America, and used for millstones; a piece of this rock.

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1690.  Lond. Gaz., No. 2538/4. Her Loading, consisting of about 750 Burr Stones. Ibid. (1708), 4501/4. A Pink … with her Cargo, consisting in Burstone, Lime, and Glasses for Windows.

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1821.  Edin. Philos. Jrnl., IV. 246. Particular account of the recently discovered Buhrstone.

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1840.  Humble, Dict. Geol. & Min. (1843), 35. The substance of burrh-stone, or mill-stone, when unmixed is pure silex.

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1850.  Lyell, 2nd Visit U.S., II. 9. This burr-stone … constitutes one of the members of the Eocene group.

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