These millstones, made of New England granite, were used to grind grain into meal, a fine powder for baking and cooking. In a gristmill, millstones work in pairs, like scissor blades, with the grooved surfaces facing each other. Grain is fed through the hole in the top stone, which turns while the lower one is stationary. As the sharp-edged grooves cross one another, they shear the grain into a fine powder.