Abrasive grain, 60/90 grit is a silicon carbide grit usually used as the first step in tumbling for agates, jaspers, etc. The five pound package is discounted at 10%. Remember when tumbling in the course grit stage (60/90) to use approximately 1 level tablespoon of grit per pound of rock in the tumbler. New grit should be added on a weekly basis since the course grit breaks down. Any other higher grit type does not need new grit added.