Gritstone's a sedimentary rock composed of coarse sand grains with inclusions of small pebbles. It's a coarser version of sandstone. As gritstone's a fluvial sedimentary rock it frequently shows signs of cross-bedding or current bedding. It's quarried for building material. British gritstone was used for millstones to mill flour, grind wood into pulp for paper and grindstones to sharpen blades. The Millstone grit's a stratigraphic gritstone unit exposed in the Peak District of north central En… (More on Gritstone)