As a crystalline variety of quartz, rock crystal can be polished to a very high luster but many people who tumble it in pieces over about one inch in size experience a problem - tiny bruises around the edges of their tumbled stones. These bruises are caused by quartz-to-quartz impacts within the tumbler barrel.

What stones should not be tumbled?

The best rocks for tumbling are hard, dense, smooth rocks such as quartz, agate, jasper, tiger's eye, and aventurine. Other popular tumbling rocks include obsidian, hematite, petrified wood, feldspars, dalmatian stone, and moonstone. Avoid tumbling rocks with a gritty texture or that are too soft.

What rocks should be tumbled together?

Some of the rocks that are commonly tumbled nicely are jasper, agate, moonstone, laps lazuli, obsidian, petrified wood, amethyst, tiger's eye, or other varieties of quartz. However, not every type of rock is suitable for tumbling. As a beginner, it is better to stick to quartz and agates.