geode - hand/display specimen of a multiple bubble filling or hollow geode
Geodes are bubble fillings that weather out of a vesicular basalt. As the basalt 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 void. In the basalt, the immediate zone around the now crystal lined bubble is altered and becomes more resistant than the basalt of the flow. These mineral lined geodes weather out of the basalt. Often they are completely mineral-filled. These show a particularly bubbly surface.
These are good examples of the bubble-filling origin of geodes. Because they are more expensive to ship, we are pricing them as hand specimens, economically purchased with other specimens that can ride in the same box. One is open with a quartz partial filling. The other is an example of what forms when multiple gas bubbles are touching in the hardened lava flow.
We don't have locality data other than "Mexico."
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