geode - bubble-filling geode - large hand/display specimen the ash and rock fragments

the ash and rock fragments were welded together

Transparent in thin sheets

The Allison Member of the Upper Cretaceous Menefee Formation is a cliff-forming yellow brown sandstone

in part because of the varied clasts

the faces of gemmy smoky quartz crystals in a cluster are polished

geode - bubble-filling geode - large hand/display specimen the ash and rock fragmentsGeodes are bubble fillings that weather out of a vesicular lava. As the flow cools, unescaped gases form voids in the otherwise solid flow. Subsequent hydrothermal activity fills these voids with mineral rich hot water and as it cools, crystals grow on the surface of the roughly spherical opening. In the lava flow, the immediate zone around the now crystal lined bubble is altered and becomes more resistant than the surrounding rock and subsequently