geode - hand specimen teaching set of geodes weathered from a Mexican lava flow

$ 7.50

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 eventually weather out of the basalt.

These geodes are best left unopened, as the quartz crystal lining is often unspectacular, and just as they are, these geodes get across to students that these are bubble-fillings. They look bubbly. We don't have locality data other than "Mexico." 

These sets ship in a Regional Priority Mail box and can be combined in that box with other purchases to save on postage.

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