Create your own crystal geode a round rock containing a crystal-filled cavity. First, cast a plaster geode shell in the mold and then fill it with a crystal-growing alum salt solution. The crystal solution contains an ultraviolet-luminous pigment that gets incorporated into the crystals as they form, resulting in a geode that glows in ultraviolet light. An ultraviolet flashlight with holder, as well as a display stand for the geode, are included. Display your beautiful specimen day and night! Learn about how crystals form and why the pigment glows under ultraviolet light.