Description
- Geode (Cut in half and polished)
- Middle Jurassic Age
- Found in Brazil, South America
- Specimen measures 2.35″ wide across the opening
Geodes were formed about 160 million years ago. As the Atlantic Ocean opened to split Africa and South America, the shifting tectonic plates triggered one of the world’s most significant volcanic events. Igneous rock flowed out of the rift, layering lava thousands of feet thick. It resulted in gas bubbles and lava tubes that hardened into cavities.
Then water entered the equation. Silica-rich water penetrated the cavities and ran through them, leaving behind the start of crystalline growth. The tiny crystals clung to the inner walls of the bubble. Thousands of years passed, then millions. Slowly, layers formed inside. First came agate, and then layers of quartz. Rock crystal grew larger with jagged points. Still buried deep inside the earth, radioactive minerals in the surround basalts began to decay. The geodes were irradiated, producing color centers in the quartz that transformed into colorful crystals like amethysts.
