The word geode is derived from the Greek word Geoides which means
"earthlike." A geode is a sphere shaped rock which contains a hollow
cavity lined with crystals. Geodes are created in the hollow areas of
soil such as animal burrows or tree roots. They are also formed in
the bubbles in volcanic rock. Over time, dissolved minerals seep into
a hollow area and harden into an outer shell creating the geode. The
minerals continue to form on the inside walls of the shell, growing
towards the center. The most common dissolved mineral is quartz, but
amethyst and other minerals are also found. A geode which is completely
filled with crystals is called a nodule. Agate-filled nodules are
called thunder eggs. Geodes are found throughout the world, and many
are concentrated in deserts. Volcanic areas are a common place to find
geodes. In the United States they can be found in California, Arizona,
Utah, Nevada, Illinois, Missouri, Kentucky, and Iowa. In fact, the geode
is Iowa's state rock. Geodes can form in any cavity that is buried. These
can be gas bubbles in igneous rocks, pockets under tree roots, vesicles
in lava after a volcanic eruption, or even in animal burrows. Over time,
the external wall of the cavity hardens, and dissolved silicates and/or
carbonates are deposited on the inside surface. Over time, this slow feed
of mineral constituents from groundwater or hydrothermal solutions allows
crystals to form inside the hollow chamber. Then the geode makes its way
back to the surface through normal geologic processes. Geodes are common
in some formations in Indiana, Iowa, Missouri, Kentucky and Utah (in the
United States). They also are common in Brazil, Namibia and Mexico. A
large geode roughly the size of a minivan was discovered in Put-in-Bay,
Ohio in the early 20th century. It is known as Crystal Cave, and tours are
possible during the summer. A thunderegg is a type of rock similar to a
geode but formed in a rhyolitic lava flow and found only in areas of
volcanic activity. Thundereggs are rough spheres, most about as big as a
baseball. They look uninteresting on the outside, but slicing them in half
may reveal highly attractive patterns and colors valuable in jewelry.
According to native legend, the Thunder Spirits lived at the highest
reaches of Mount Hood and Mount Jefferson, and when they became angry
at each other, they threw these spherical rocks at each other. It is
the state rock of Oregon. (from Wikipedia, the free encyclopedia)  The
hostile gods obtained these weapons by stealing eggs from the
Thunderbirds' nests, thus the source of the name "Thundereggs." 

If you feel the urge to mine your own geodes in Utah here is some info.  We have been to this location several years ago, and pickings were fair, and digging not too hard. 

From Salt Lake City take I-80 westbound until you reach the Tooele turnoff (exit 99). Travel south on Highway 36 for approx. 40 miles to the Pony Express Road (dirt road). Turn west (right) and proceed approx.50 miles on the Pony Express Road to the Dugway geode bed turnoff (sign may be missing). Turn north (right), proceed up the dirt road and look for recent diggings.

Where to collect: Geodes can be found approx 1 to 2 miles north/northeast of the turnoff.  You will be digging in a soft, unconsolidated material that is susceptible to caving, so please be careful!

The geodes are fairly easy to recognize due to their round shape and light weight.

Land ownership: Bureau of Land Management (BLM) public lands. Active mining claims exist on some portions of the "geode area" so seek permission from the claim owners before collecting.

BLM collecting rules: The casual collector may take small amounts of gemstones and rocks from unrestricted federal lands in Utah without obtaining a special permit if collection is for personal, noncommercial purposes. Collection in large quantities or for commercial purposes requires a permit, lease, or license from the BLM.

Tools recommended: shovel, pick, safety glasses and hammer. Bring plenty of water.  We would not recommend this when raining or roads are muddy, and another tip make sure you have a good spare tire. This area is miles from anywhere and you would not like being stranded here.
Have fun collecting!

                  Questions email us at     cushman55@charter.net          We will answer your questions if we can.