A rock tumbler is a device used by lapidarists to shape and polish the rocks that they work with. A lapidary is someone who works with rocks, either as a hobby or a profession. Hobbyists may use a rock tumbler to polish rocks that they have collected for display, while professionals such as jewelers use a rock tumbler to shape and prepare rocks in preparation for use in finished pieces. Because of the wide range of people using rock tumblers, they come in an assortment of styles ranging from simple desktop models for people just experimenting with rock tumbling to industrial models for use in large jewelry studios.

When rock is first mined or collected, it is usually rough, misshaped, and pitted. A skilled lapidary can see the potential of a hunk of rock like jade or quartz, and use a rock tumbler to bring out the natural beauty of the stone. First, the rough is broken into chunks of different sizes, and then put into a rock tumbler with coarse grained grit. The tumbler is a cylinder which turns with the assistance of a small motor. After several days have passed, the rocks are checked, and if the lapidary is satisfied, they are washed and tumbled with a smaller grained grit. This process is repeated several times, with the grit getting progressively finer, until the stones are ready for polishing in a rock tumbler set aside specifically for this purpose. When the rocks emerge, they will be much smaller than they were originally, but they will also be polished and glowing with the natural beauty of the stone.

As a hobby, rock tumbling calls for a great deal of patience and a workspace which can be soundproofed, because rock tumblers must run for a long time before the rocks are completely polished. A rock tumbler essentially speeds up the natural processes of nature, which will polish rocks eventually over centuries. Even with a rock tumbler, however, turning a piece of rough into a polished specimen can take several weeks.

A basic rock tumbler works through rotation, but some lapidary supply companies make rock tumblers which use ultrasound or vibration. These tumblers tend to be more costly, but they are also quicker and more quiet, and produce a range of rock shapes as well. Ultimately, the choice of what type of tumbler to get is up to the individual purchasing it. If you are considering rock tumbling as a hobby, you may want to consider acquiring a tumbler designed for small rocks until you have decided whether or not tumbling is for you, at which point you can purchase more costly big tumblers which can handle more weight, and bigger rocks.