Agate Geode, Brazil

An agate geode is a hollow agate lined with tiny quartz crystals. Agate geodes are formed in gas bubbles in lava. After the lava hardens around the bubble, water seeps through and deposits silicates and/or carbonates on the inside surface. Over time, this allows quartz crystals to form inside the hollow chamber. Bedrock containing geodes eventually weathers and decomposes, leaving geodes present at the surface. Agate geodes are found in Mexico, Brazil, Morocco and India.