Geology.com reminds us about the fun of rock tumblers:

Rock tumblers have been manufactured and sold to hobbyists since the 1950′s. The first machines tumbled rocks in metal cans. Since then rubber barrels have significantly reduce the noise, however rotary machines still require at least one month to convert rough rock into brightly polished stones. However, newer vibratory tumblers can process rock in a little over a week.