Rag-Stone, a genus of siliceous fossils, discovered in various parts of Britain. It is of a greyish colour ; contains a large proportion of particles resembling talc; and splits easily into thin scales. It effervesces with acids ; and, though very soft, emits fire, when stricken, against steel.—This mineral is employed by artificers for the purpose of giving a fine edge to knives, chissels, and other tools, which have previously been sharpened upon stones of a coarser texture.