Utah Dugway Geode | Closed Mine

Specimen Measures approx: 2.75" x 2.5". This particular mine is no longer being mined for these geodes. Composed of rhyolite, agate and quartz, these beautiful hollow geodes were formed from volcanic activity... They began as hollow 'Lithophysae' (Rock Bubbles) produced within the flow of molten rhyolite rock as it surfaced and began to flow above ground. As the flowing molten rhyolite began to cool. Cristobalite and Perthite from within, crystallized into ball or button-shaped "Spherulites'. Some of these spherulites, upon reaching maturity, expelled a flash of hot gas creating a star-shaped bubble. The size and state of development of the bubble are related to the size and depth of the spherulite at the time of its firing. Those closer to the surface face less pressure from the overburden weight of the molten rock above, and produce larger gas cavities. Those deeper down may only manage to develop a small arch-shaped cavity. Some are duds and never de-gas. The rock bubble becomes buo