Quarried in Belgium; these Belgian Clay Wet Stones from Pfeil Tools are a course to medium grit natural wetstone but do have natural variations. Used with water they remove material rather quickly for resharpening cutting edges.Two sizes available: The BB6 is approximately 40 square centimeters and BB8 is approximately 60 square centimeters but these stones can vary in shape; ranging from triangular to rectangular and any other form in between.