1. A hard, porous stone used to make millstones for grinding grain.
Usage: Also spelled 'burstone' or 'buhr'.; Historically important in milling.
2. A type of siliceous rock composed of fossilized diatoms, quarried especially in France and Germany.
Usage: Technical/geological usage.

Examples

• The miller selected a buhrstone for its durability and fine grinding properties.
• Buhrstone was imported from Europe to equip American mills in the 19th century.
• The porous structure of buhrstone made it ideal for milling flour.
• Quarries in France produced high-quality buhrstone for export worldwide.
• Old buhrstone millstones can still be found in restored historic mills.