A geode is a hollow rock formation, often spherical or ovoid, that develops inside volcanic or sedimentary rocks. What makes it unique is its interior lined with crystals, such as quartz or amethyst, ...

Slowly, these minerals crystallize, forming a dense lining of quartz or other silicates that can include a variety of crystals like amethyst, calcite or celestite. When a geode splits open ...

They develop when groundwater rich in silica flows through rock and begins building up layers of quartz. If the developing ...