Geodes 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 weathers out. Often they are completely mineral-filled. Some are hollow.
These geodes are best left unopened, as the quartz crystal lining is often unspectacular. They get across to students that geodes are bubble-fillings. They look bubbly. We don't have locality data other than "Mexico." Jumbo textbook example.
Two views of the same specimen. The pencil is 5 1/2" long, for scale.
Shipping: By Priority Mail or USPS Ground Advantage, whichever is cheaper, unless we find a better rate. Click > here < for shipping rates. See comment at Note! Use back button to return to this page.
Making multiple purchases? Click on the "combine shipping" button in the shopping cart. We'll send an invoice with combined shipping. A link in that invoice will bring you back to checkout, no hassle.
