Geodes are round, hollow geological rock formations commonly of sedimentary or igneous rock. The interiors are often lined with quartz crystals. Prized by rock hounds and used for decoration and jewelry, they are found in many parts of the country. Idaho, the Gem State, has its share of geodes. For those prepared for rock hounding in Idaho's scenic, rugged and mineral-rich back country, there is a supply of geodes available.
Locate areas in Idaho where geodes are likely to be found. There are several books available on the minerals of Idaho and where they are located. You can also go to the Idaho Department of Lands website under "Gemstone and Rock" information for a list of gemstones by county. See the Resource section for more information.
Acquire detailed maps of the area you wish to search for geodes. Sources of maps include the Bureau of Land Management, U.S. Forest Service and Idaho Department of Lands. These will help you find your way in and out of an area. The Idaho Geological Survey has maps showing the geological details of an area, which is useful in determining where geodes might be located.
Locate good hunting areas once you reach your destination. Look in volcanic ash beds, and also check gravel deposits and rock formations containing limestone. Geodes congregate in "beds," and most will be found in the rocky, desert areas of Idaho.
Search the ground for round, lumpy rocks. Distinguish them from other rocks by their shape and by weight. Since they are hollow, see if a round lumpy rock feels lighter than you would expect. Shake it and listen for a rattle made by a loose bit of crystal. Most geodes will be from marble to softball size, although much larger ones are found.
Dig with your shovel or pick. If you are in an area popular with rock hounds, it might be harder to find surface rocks. Also, geodes on the ground indicate more below the surface. You your pick or rock hammer to loosen potential geodes from rock formations.
Confirm geodes by breaking a few open with your rock hammer, looking for hollow interiors and crystal formations. Save most to take to a professional for cutting and polishing.
According to the Gemstone Guide on the Idaho Department of Lands website, quartz-lined geodes can be found in the upper valley of Lost River in Custer County, near the DeLamar Silver Mine in Owyhee County, and northwest of the town of Weiser, Idaho in Washington County.
Usually no permits are needed for amateurs to collect rocks on Idaho public lands. Some areas are restricted for other reasons, however, so check with the department that has authority over the area. Always get permission before collecting on private property.
Follow the "Rockhound's Code of Ethics," which includes respecting private property, closing gates and leaving no trash. A copy of the code can be found on the Idaho Department of Lands Gemstone guides web page.