Collection: Thunder egg

thunderegg is a geode-like geological structure that forms in silica-rich volcanic rock, often rhyolite. Its core is typically filled with chalcedony, agate, opal, jasper, or quartz, but may also contain quartz and gypsum crystals, or other mineral inclusions. The outer shell is usually a volcanic rock, and the central cavity can be filled with mineral deposits in layers, creating intricate patterns.