Geodes are hollow rock formations often with quartz crystals, such as amethyst, inside. Amethyst geodes in Uruguay have been found in cooled lava flows, which date from the original breakup of the ...

Liquid-filled rocks form when minerals trap fluids, but depending on their composition they can either be classed as enhydros, enhydro agates, or fluid inclusions. An enhydro is a hollow nodule that ...