Geodes are hollow, usually rounded cavities in a rock that are lined with crystals and other minerals. They are typically formed in igneous (volcanic) rock, though they can also be present in sedimentary rocks.
How Do Geodes Form?
Geodes typically start out as hollow gas bubbles in volcanic rock. Over time, hydrothermal fluids or groundwater deposit minerals within these gas bubbles, forming a crystal lining. Read more...
What Minerals/Crystals Are Found In Geodes?
By far the most abundant mineral found within geodes is macrocrystalline quartz (including amethyst), but calcite, pyrite, barite, celestite, & chalcedony (agate) are also frequently found. Geodes found at the same locality typically have similar minerals deposited inside.
What’S The Difference Between A Geode, Nodule & Vug?
Geodes are hollow cavities within the rock, while nodules are completely filled in with minerals. Vugs are irregularly shaped pockets typically along of vein or breccia while geodes are rounded or oblong in shape.
Where Are Geodes Found?
Geodes have been found in volcanic rock world wide, but some of the most prolific deposits include:
The Dugway geode beds in Western Utah.
The Warsaw Formation in the Keokuk region near the area where Missouri, Iowa, and Illinois.
The volcanic rock deposits in Southern Brazil and Uruguay which produce gorgeous and sometimes very large amethyst geodes.
The area near Chihuahua, Mexico produce abundant geodes called Coconut Geodes mined from about 100 feet below the surface.
What Is The Largest Geode Ever Found?
There are two geodes that ">lay claim to be the world largest, a massive, 35 foot across Celestite geode in Ohio and the 30 foot long, selenite crystal lined, Pulpi Geode in Spain