Geode
A geode is a hollow, rounded rock that contains an interior lining of mineral crystals, often contrasting with a plain or rough exterior. Geodes most commonly form in volcanic or sedimentary rocks as mineral-rich fluids crystallize inward over time. The most common crystal compositions include quartz, chalcedony, and amethyst, with calcite also frequently present. Chemically, geodes are typically composed of silica (SiO₂) or calcium carbonate (CaCO₃), depending on their dominant minerals.
