This is where the rough material is put in a revolving barrel with abrasives. Progressively finer abrasives are used, until a polish is obtained. This process closely resembles what happens to rocks in a stream or on the beach, except that the level of polish is much higher. Tumbling is ideal for children. There are a number of inexpensive settings available so the tumbled stones can be turned into jewelry.
Cabs are gems that are cut with a flat bottom and a curved or domed top.
If you can envision an opal or a piece of turquoise, you are looking at a cab. Cabs have distinct resale value, based on the material they are cut from and their cutting can be profitable. This makes for an excellent, indoor hobby. It only takes a little practice to become proficient and is something almost everyone can learn to do well. If you can envision a diamond, you are looking at a faceted gem.