If you enjoy taking something dull and making it shine, then polishing cut rocks can be a rewarding pastime. While all rocks can be polished by hand, rocks that rate 4 or higher on the Mohs hardness scale (see Resources for a link to determine rating for your rock), a lapidary tool such as a flat lap or rock tumbler, which will do the work for you. To polish a cut rock by hand, all you need are a few tools and a lot of time.
File or chisel sharp corners and deep depressions to make them smooth. Continue filing until the rock is in the basic shape you want it to be.
Smooth away any imperfections in the surface of the rock with coarsest sandpaper, grade 50. Sand the rock in a steady rotating motion, by holding in one hand and turning it as you sand with the other.
Sand the rock with finer grade sandpaper, beginning with the 100-grade paper and progressing up to 400, with the same motion as described in the earlier step. Sometimes at 400 and above, it helps if you wet the sandpaper down. However that it will get a little messy. This step should remove all the scratches from the earlier papers.
Sand your rock with 600-grade sandpaper. Again, wetting the sandpaper will work best. Get all the marks from the sandpaper out in this step. Once it looks smooth, let it dry, and check it for any scratches or imperfections. If there are any, then go back to the coarser paper and start again.
Put a small amount of polishing powder on a dampened piece of leather or velvet, and rub the rock in tight little circles. Rotate all around the rock as you work. Once you have done the entire rock, wash it off. You now should have a beautifully polished rock for your collection. If any scratches appear after polishing, go back to the 400-grade sandpaper and begin again.
If you decide to use lapidary equipment to polish your rock, be sure to closely follow the manufacturer's instructions. Also, give the barrels or trays (depending on the type of machine you have) a thorough cleaning between each phase; otherwise the rock may become marred during the polishing phase, making it necessary to start over.