It is important that you select stones that will polish in order to be successful at tumble polishing. The looks of rocks can be deceiving, but in general, those with a hard surface and sometimes shiny look to them, are likely to polish.

Stones with hardness of around 5 to 7-1/2 on the Moh Scale of Hardness are best. This includes the agates and jaspers which are the easiest to polish. Softer and harder stones, and certain stones such as Apache Tears and jade are special challenges, and require special procedures.

Listed below is the Moh Scale of Hardness which rates minerals on a scale of 1 to 10, with No.1 Talc being very soft, and No.10 Diamond the hardest of all. A mineral with a high number can scratch those with lower numbers.