You might be surprised to learn that some people have found geodes with fluorescent minerals inside. Some of the Dugway geodes, found near the community of Dugway, Utah, are lined with chalcedony that produces a lime-green fluorescence caused by trace amounts of uranium.

Dugway geodes are amazing for another reason. They formed several million years ago in the gas pockets of a rhyolite bed. Then, about 20,000 years ago they were eroded by wave action along the shoreline of a glacial lake and transported several miles to where they finally came to rest in lake sediments. Today, people dig them up and add them to geode and fluorescent mineral collections.