Mama's Minerals brand 150/220 Silicon carbide is a high-end lapidary grade abrasive perfect for lapping or tumbling. This 220 grit is good for the second step in the tumbling process and used for medium/fine lapping. Especially useful for getting a high polish while tumbling glass.1 lbs. 150/220 grit Will tumble approx. 10 lbs. rock.