Rock polishing machines are noisy and tumble rocks together to create a smooth and shiny surface. You can create similar results without this machine. A Dremel tool with a grinding attachment offers one solution.
Place the rock inside the clamp so you can reach a good portion of it. Holding the rock in a clamp helps prevent the possibility of grinding your fingers as you polish.
Attach the lowest-grit sanding bit. Plug in the Dremel. Grind the entire surface of the rock with the grinding tip. Use just the top half of the bit to prevent deep scratches. Angle the tool as flat against the rock as possible to grind away rough edges evenly.
Switch to the 800-grit bit and continue to grind the entire rock. Grind with progressively finer bits until the rock starts to shine. Move it inside the clamp to expose the rough edges, and grind them down in the same way.
Polish the surface of the rock to a high shine with a polishing cloth and a small amount of polishing compound. Buff the polishing compound into the surface of the rock for several minutes. This reveals the natural luster of the rock.