The Exotic Beauty of Geodes

The thrill of finding geodes has attracted rock hunters for centuries. Hunters look in desert areas that have deposits of volcanic ash and limestone. Hunters have found beds along rivers where the water has worn through layers of earth to reveal deposits left during early eras.

Geodes are crystal formations inside rock spheres. They are hundreds of millions of years old. Geodes may have formed from the inside out or from the outside in. Some scientists say gas bubbles formed a pocket in the surrounding magma. The resulting void was washed with water containing minerals that were left there and formed crystals. Other scientists say the nodules formed around a nucleus that was found in soft sediment. The outer shells of the nodules were replaced by chalcedony (quartz). The inner portion was dissolved away which provided room for the quartz crystals to grow.

Geodes are also known as thunder eggs. They are found on desert floors in plain view. They are found in rock ledges. They are found in rock hard volcanic ash beds. In Iowa, they are found along stream drainages. The geode rocks are lighter in color and weight less than the other rocks in the area. They range in size from a cherry to a minivan. Most will be no larger than a grapefruit.

Geodes are hollow. If the center is completely filled, it is a nodule. Geodes are spherical and the outside may appear lumpy and resemble a cauliflower. The crystals are usually quartz. There can also be kaolinite, dolomite, pyrite, iron sulfide, sphalerite, black agate, opalite, and calcite. The mineral content and colors vary based on the location where the geode formed.

For those planning on a rock hunting expedition, suggestions for what to bring include: bucket for the geodes, shovel, hand pick, safety glasses, hammer, plenty of water, food, a spare tire for your vehicle, map of the area, flashlight, GPS, drill, pry bar, work gloves, four-wheel drive, hat for shade, and sunglasses. Dress appropriately for the day and evening weather conditions. Most bed sites are in remote areas. Plan to leave the area well before nightfall.

There is more advice from experienced hunters. Be on the lookout for mountain lions and snakes, depending on the area. Do not enter or remove rocks from private land without expressed permission from the owners.

Geode sites are found in California (Hauser Beds, Potato Patch, North Black Hills, Hidden Saddle Beds, Straw Beds, Cinnamon Beds), Iowa (Keokuk, Geode State Park in Henry County), Arizona, Missouri, Indiana, Kentucky, Nevada, New Jersey, New Mexico (Rock Hound State Park in Deming), Ohio (Crystal Cave), Oregon, Texas, and Utah. There are numerous books available to help rock hunters locate the precise area they want to explore. The more heavily traveled areas will usually mean smaller geodes. The lesser traveled areas will be more remote and inaccessible.

Sources

Two Guys Fossils, http://www.twoguysfossils.com/oddity.htm
Desert, USA, http://www.desertusa.com/magjan98/jan_pap/du_rock_geode.html
Desert, USA, http://www.desertusa.com/magjan98/stories/hauserbeds.html
Desert, USA, http://www.desertusa.com/mag05/sep/rocks.html
Desert, USA, http://www.desertusa.com/mag05/nov/cinn.html
Utah Geological Survey, http://geology.utah.gov/utahgeo/rockmineral/collecting/rkhd0500.htm
Iowa DNR Geological Survey, http://www.igsb.uiowa.edu/browse/geodes/geodes.htm
Treasure Hunting for Geodes, http://www.articlesbase.com/destinations-articles/treasure-hunting-for-geodes-434577.html