This is an amethyst geode — a hollow rock lined with purple quartz crystals that formed over millions of years. It starts when gas bubbles get trapped in volcanic lava. Later, mineral-rich groundwater seeps inside. As the water slowly cools and evaporates, silica and trace iron crystallize along the inner walls. Natural radiation in the surrounding rock then changes the iron atoms’ structure — giving amethyst its signature violet color. What looks like a simple rock from the outside can hide perfectly ordered crystal structures on the inside. Nature doing materials science long before humans studied it. Would you crack one open or keep it sealed? Comment below and tag someone who loves geology. #stemantics #geology #crystals #amethyst #geode