Inspect the rough stone by wetting with water under a bright light. Direct light is ideal. (The stone is fragile so hold it over a padded surface). Observe the depth and location of color layers. The gem material (fire layer) is usually covered by chalcedony. Trim away excess chalcedony by sawing, grinding, or sanding. Sawing
Geologic information: Approximately 6 to 8 million years ago (Miocene epoch), volcanic activity occurred in western Utah and deposited an extrusive igneous rock called rhyolite. Trapped gasses formed cavities within the rhyolite, and millions of years of ground-water circulation allowed minerals to precipitate into the cavities. The result is geodes with spherical shapes and crystal-lined cavities.
by Geologic Information and Outreach Staff Utah Geological Survey Utah’s rock, mineral, and fossil collectors must adhere to rules and regulations established by owners or managing agencies of the lands on which they wish to collect. Prior to collecting, rockhounds should determine ownership of the lands they intend to visit and familiarize themselves with the