Two Pounds, 25-30 Whole Dugway Geodes • 0.5\" to 1.5\" diam. For Sale

Dugway Geodes

Crystal Filled Volcanic Gas Bubbles from the West Desert of Utah

What is a Dugway Geode?

Dugway geodes are bubble-shaped rocks that have a hard outer shell composed of agate called a rind. Inside the agate shell is a hollow cavity filled with small crystals. The most common mineral found in geodes is quartz in various colors: clear (rock crystal), purple (amethyst), and pink (rose). Geodes occur in deposits all over the world and each one has it’s own unique characteristics, colors and patterns depending on the geology of the area where it is found. As for Dugway geodes, the only place in the world where they can be found is in western Utah.

Collecting Location: & Age

These specimens come from the Dugway Geode Bed, which is located just north of the historic Pony Express trail in a small valley near the Dugway Mountains in Juab county, Utah. The geodes were formed during the Miocene Age, approximately 6 to 8 million years ago.

How Are Dugway Geodes Formed?

These geodes started out as gas bubbles trapped in ancient lava flows. To understand their origin you have to go back 6 to 8 million years when volcanos were very active in western Utah. During this time the Thomas Range and Dugway Mountains were formed as rhyolitic lava repeatedly erupted on to the surface of the Earth. As the lava cooled gas bubbles of all different sizes got get trapped inside the lava.

Now you have bunch of bubbles trapped in your lava, what’s next? They slowly get filled with minerals. This happens when groundwater, saturated primarily with calcite and quartz, percolates down from the surface and is deposited in the cavitates. The term for this process is precipitation and the result is a crystal-filled, volcanic gas bubbles or, more formally, geodes.

How Were the Dugway Geodes Beds Created?

You now have bunch of beautiful geodes buried in the lava deposits on the sides of the mountains. The next question is, “How did they wind up on the valley floor? Jump in your time machine and go back approximately 32,000 to 14,000 years. You will find that an ancient body of water, known today as Lake Bonneville, covered a good portion of western Utah. The wave activity in the lake eroded the geode-bearing rhyolite in the mountains, loosening the geodes from the rock. Once free from the rock the geodes were washed downhill and redeposited several miles away with other lake bed sediments. You can see this first hand when you dig in the bed. You will find that there are several distinct layers of geodes present and each layer represents a different time in the history of Lake Bonneville. Geodes have been found as deep as 65 feet below the valley surface.

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