RAGSTONE

n.A stone of the silicious kind, so named from its rough fracture. It is of a gray color, the texture obscurely laminar or rather fibrous, the lamins consisting of a congeries of grains of a quartzy appearance, coarse and rough. It effervesces with acids, and gives fire with steel. It is used for a whetstone without oil or water, for sharpening coarse cutting tools.

ragstone

rag |stone |ˈragstəʊn | ▶noun see rag 3 ( sense 2 ).