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 you not tumble?

Rocks NOT to Tumble

Metamorphic rocks that contain micas or have a "grainy" texture are also unsuitable - they will break up instead of becoming smooth. And, most igneous rocks do not tumble well because they contain several different minerals that wear down at very different rates.

Can agates be tumbled?

Agate is the most popular tumbling rough because it often has great color, interesting patterns (bands, eyes, moss, lace, fortifications), translucence, and it usually accepts an exceptionally bright polish. It is usually easy to polish and is a great tumbling rough for the beginner.