Eye agate is a type of agate that exhibits one or more round concentric markings known as "eyes." These eyes can be of different colors, including brown, black, white, blue, and green. Eye agates are formed when silica-rich water seeps into cavities in volcanic rock and deposits layers of agate. The eyes are formed when the water contains different minerals, which gives the agate its characteristic banding.
Eye agates are formed when silica-rich water fills a cavity in a rock. The silica then precipitates out of the water, forming layers of agate. If the silica-rich water contains impurities, such as iron or manganese, these impurities can create the concentric markings that we see in eye agates.