Trancas Geode under UV light greeting card

Greeting card (blank inside) of a rock specimen, the Trancas geode (a.k.a. Chihuahua geode), from the collection of artist J. Mummey. Trancas geodes put on a spectacular show when exposed to short wave UV light. Chraacterised by their dazzling white drusy crystalline centres, these geodes contain a very small amount of uranium that often fluoresces a brilliant bright-green. Prized for their drusy quartz interiors, and their distinctive green fluorescence under short wave UV, they are generally small and are approximately 37 million years old. These were formed as gas cavities in volcanic rock that later filled with silica rich fluids, producing quartz and chalcedony.