This Large Mineral Specimen Comes with a Fact Filled Information Card. These nifty geodes are every little boys' dream and are great for hands on learning of basic Earth geology. Crack these geodes open and find out what's inside! Each cystoid geode comes with free geological info and safety instructions. A cystoid geode is now an extinct animal that lived at the bottom of ancient seas 438 to 408 million years ago. When a cystoid died, its body was covered with sand and sediment on the ocean floor and sometimes became fossilized. When the cystoid became fossilized, it also became a rock with a hollow center geologists refer to as a geode. When the seas receded, the hollow cavity of the fossilized cystoid became filled with silica-rich ground water that caused quartz to form inside.
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