What are Purple Amethyst geodes?
Geodes and in particular amethyst geodes are fascinating members of the quartz-crystal family. Tall purple/violet geodes are usually called amethyst cathedrals. Geodes are usually formed in “bubbles” and other cavities in volcanic rock, especially molten rock that has intruded into other preexisting rock layers. (They can also form in surface lava flows that are thick enough so that cooling is slow.) After an intrusion of molten rock is in place, it gradually cools and hardens. Various minerals crystallize out at different temperatures so that part of the intrusion is still liquid while other parts have already solidified. Molten rock also contains large amounts of dissolved gases. As the rock cools, these gases come out of solution and form “bubbles” and cavities in the rock.
