... sandstone,marble,and other soft metal materials. 6''x2''x2'' Green Silicon Carbide Rubbing BrickA very low-cost tool to grind & sharpen sandstone ... ,soft metal materials,etc.Made up of GC (short for Green Sillcon Carbide),an abrasive material softer than Diamond & Aluminum Oxide. Size ... :T/T,L/C,Wetern Union,etc. 6''x2''x2'' Green Silicon Carbide(GC) Rubbing Brick for Stone