Geodes are hollow rock formations often with quartz crystals, such as amethyst, inside. Amethyst geodes in Uruguay have been found in cooled lava flows, which date from the original breakup of the ...

Opinions expressed by Forbes Contributors are their own. David Bressan is a geologist who covers curiosities about Earth. “We were thrilled!” said Dr. David Grant, a researcher at the ...

But they’re not exactly the same thing. Geodes typically have a hollow cavity lined with crystals. They form in sedimentary rocks like limestone, where mineral-rich water flows into cavities ...