Aluminum oxide, pre-polish, 800 grit is highly recommended by tumbling experts as a pre-polish for tumbling (after the 500-600 Fine grit stage). Particle size is 800/mesh/grit or about 20 to 25 micron. It is a hard brown fused aluminum oxide basically spherical in shape. An order of one is a one pound package. You will find aluminum oxide is tougher than silicon carbide though not as sharp and thus breaks down more slowly. For those of you into glass carving and etching, you will find aluminum oxide an important step. Aluminum oxide, 800 grit is a most economical pre-polish. This abrasive is good for soft and difficult stones such as Apache tears, and tigereye and works great on hard stones. Tumbling enthusiasts highly recommend this extra step in tumbling your stones for a superior polish. It is also used with metals, polishing findings, etc. The amount to use in your tumbler is as with other grits: one tablespoon per pound of material. Remember to keep experimenting and keep a notebook for your tumbling process to get the best results. New information and procedures have dramatically changed over the years.