Silicon carbide, abrasive grain, grit size 150/220 is normally the second step in tumbling stones such as agates and jaspers. (Medium grit stage.) If tumbling a soft stone, grit 150/220 will be the first grit to use in the tumbling process. Use one tablespoon of the silicon carbide abrasive grit, 150/220 per pound of rock in your tumbler. An order of one is for one pound of silicon carbide grit size 150/220.