Geodes in Arizona are typically located in deserts, areas with large quantities of limestone or volcanic ash beds. In order to find specific locations of geode beds, consult with a local desert or rock authority, such as university science officials or members of an archaeological or geological society.
A geode is a hollow mineral body that is found in a few shale types and in all limestone types. Most geodes are partially flattened and in the shape of a globe. They can range in size from a 1 inch to 12 inches in diameter. The hollow interior of the geode has crystal layers that grow on top of one another. These crystals are often made out of quartz, but can also be made from dolomite, calcite, ankerite, aragonite, magnetite, hematite, pyrite, sphalerite or chalcopyrite.
When a person goes looking for geodes at a geode bed, it is called prospecting. Scientists and geologists have had a difficult time explaining the formation of geodes because they can be formed through several different means, although all initially begin as bubbles in either animal burrows, mud balls, tree roots, sedimentary rock or volcanic rock. Geodes are also similar to nodules. The only true difference between the two is that the nodule is completely solid while the geode has the hollow cavity with crystals.