we unearthed a geode and opened it with a rock hammer (relax we have many more geodes). Within the crystal lined cavity is a great deal of empty space. Do these spaces contain very old air or gasses or what? Or are they vacuum sealed? What’s with the air inside of an extremely old hollow rock?
I think it’s still a little bit of a mystery as to how geodes are formed. but it’s believed they are basically petrified lava bubbles. The outside hardens, trapping minerals inside the bubble, which then dissolve and crystallize along the inner surface, often still leaving a hollow on the inside.
I’m more a stratigrapher than minerologist but I believe that geodes are formed in a variety of environments, from ash beds to carbonates like limestone and dolomite. I’m of the understanding that, generally speaking, they form from the outside in. High temp silicates are often present and form bands as the temperature drops as the rock cools, sequentially depositing different suites of mineral assemblages. Sometimes this can form a vacuum within the rock. If the rock is higher up in the geode bed, it can suck in air from the atmosphere. Further down in the bed, it can draw in groundwater containing more minerals that then have an opportunity to contribute further to the geode’s layering process.
Oh man, that’s rough… “mineralogist”.
A bit off topic, but how do you know a rock will be a geode?
They look pretty cool, but how do you find them, is it total luck?
MtM
It’s not air. It’s deadly, deadly poison gas. The rock has to be opened under carefully controlled conditions, or the person who opens it and gets a whiff of the contents will suddenly and mysteriously die by cerebral detonation.
No, no, no, you’re thinking of golf balls.
I had that once. Hurt like hell.
Give me tennis elbow any day.
huh. I got two words for you guys: basket balls