When is a millstone not a millstone?

This is a good site on millstones and when a circular stone (like the ones above under Stanage Edge which ARE millstones!) is not a millstone.

Millstones - used in pairs to shear grains fed into a narrow gap between their faces; used in grist mills

Quern-stone - manual version of millstones

Grindstones - used to sharpen metal cutting tools etc. pushed against their edges

Pulp stones - a special type of grindstone that was quarried in large numbers in the late 19th and early 20th centuries: exported to Canada and Scandinavia to be mounted in machines used to pulp timber for paper making

Edge runners - cylindrical stones mounted on an axle and used to crush a variety of materials and even foodstuffs as they rolled around a pivot

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