Similar to sandpaper, each stone has a different grit that will result in sharper or duller tools.
In Australia, Aboriginal peoples created grinding grooves by repeated shaping of stone axes against outcrops of sandstone.
[3] Grindstone machines work by spinning a circular piece of stone around its center point.
The earliest known representation of a rotary grindstone,[6] operated by a crank handle, is found in the Carolingian manuscript known as the Utrecht Psalter.
[7] The Luttrell Psalter, dating to around 1340, describes a grindstone rotated by two cranks, one at each end of its axle.