I’m seeing gilded-edge agate slice coasters everywhere, and they’re beautiful. They are also very expensive. For a set of four, you’ll find prices around $100–even higher at some stores.

From geodes to agate slices, Rockology Gems and Minerals has put on a display at the 22nd Street Gem Show for years. It is Tucson’s largest gem show that is free and open to the public and is ...