The Utah Dugway thunderegg geodes are collected in western Utah in western Juab County, and are approximately 6-8 million years old. These specimens are considered thundereggs and not geodes given their growth process (they are a rhyolitic mass that contains a hollow that is usually entirely filled in with quartz, agate, or quartz containing (silicified) rhyolite). Note the irregular shape (more square or star-like shapes) of the interior cavity of the Dugway thunderegg specimens compared to regular geodes - these formed under different conditions than geodes in that a cavity is not usually present unless the outward growth of minerals (due to heat) is large and forceful enough to result in a cavity. Most thundereggs from the western United States are solid or only contain small cavities, but a large percentage of thundereggs from the Dugway beds in Utah are hollow and contain a varying degree of drusy quartz lining the hollow interior. Some of these thundereggs have a non-drusy quartz (chalcedony) lining while others are completely lined with sparkling drusy quartz throughout and may also contain banded agate. Additional minerals sometimes found include calcite, quartz scepters, or small tabular barite. Some interesting quartz growths are also found in some specimens. We feel it is best to label these specimens as "geodal thundereggs". All of our Utah thundereggs are acquired directly from a claim owner in western Utah. Many of these geodal thundereggs also fluoresce bright green under shorthwave ultraviolet light due to trace amounts of uranium, just like the Mexican Trancas geodes. We guarantee all of our Utah Dugway thundereggs to be at least 90% hollow by volume, meaning 9 out of 10 thundereggs will contain an open cavity with a varying degree of drusy quartz on the inside from one geode to the next.
The Dugway thundereggs below can either be cracked or sawed open. If you are familiar with the Mexican coconut geodes, the Dugway geodes open very similarly to the Mexican coconut geodes and do take a good polish. The inside shell on these geodes is a dark brown rhyolite and quartz/banded agate nearest the interior. Typical Utah Dugway Thunderegg interiors are shown below.
UPDATE August 2016 - Any updates to this page will be very limited in the future as the primary Dugway geode claim owners recently lost their claim and commercial mining is no longer taking place. As a result, we are no longer able to acquire quantities of these geodes for resale. When they are gone, they are gone!
For opened Utah Dugway thundergg Pairs, please see the Utah Dugway Thunderegg Opened Pairs Page.