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. It is often a family activity, working with stones collected on vacation. Cutting cabochons is probably the most common form of gem cutting.
Cabs are gems with a flat bottom and a curved or domed top.
If you can envision an opal or a piece of tiger's eye, 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. Cabochon cutting is a step up in complexity from tumbling and it requires a greater investment in tools. If you have the skills you can make your own equipment, which keeps the cost down.