Geode Rocks

Have you ever seen a Geode before?

Geode3 Geode4

But do you really know what it is though? I found out yesterday that geodes are geological, that they are formed from sedimentary and volcanic rocks.

They are rock cavities with crystal formations (The inside, with time and space the crystals form) and/or concentric banding. (the rings of color around the inside)

The exterior is usually lime stone or related rock with quarts crystals or chalcedony deposits. They are really incredible and enjoyable rocks to have. But how are they formed? Where are they formed?

Yours truly,



About Bill Ferriter

I'm a real-live, bona-fide, full-time practicing classroom teacher. #takeTHAT
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8 Responses to Geode Rocks

  1. Canyon Dell'Omo says:

    From my previous knowledge, Geodes are spherical rocks that exist in other volcanic rocks (don’t ask me how those got there.) Then, pressurized steam from the volcanoe bores holes in the rock, making the hollow cavern that you see in the picture. Then, after an eruption, the rocks land and eventually make their way to a river. Here, they settle in the mud at the bottom, and water carrying crystal forming sediment flows in and out of the cavity, eventually creating the crystals inside. Thats just what I know. Those rocks are really cool though….

  2. wicked awesome monkey dude says:

    canyon, im not even gonna ask how you know that

  3. the pencil thief says:

    i can see how geodes are sedimentary rocks but how exactly does volcanic fit into this? if you’ve ever looked closely at a cracked open geode it kind of looks like ripples. you can see this clearly in your second picture above. perhaps all geodes start out sedimentary than later become volcanic, and that may be what gives them the rough outside coating.

  4. Dude, Canyon, how do you know everything in the world?
    You did a wiki page once on ‘Basic Human Genetics’.
    -The Modern Typewriter

  5. FOB says:

    Seriously….do I look like a geologist to you? I just read that from somewhere a while back. Why don’t you look it up on wikipedia or something?

    Alright…I just read some more on the topic, finding the bridge between the sedimentary rock and volcanic rock. Through a process called lithification, the fragments and sediments are compressed into solid rocks, which could be any of the three types of rocks. In this case with them being sedimentary, which are then melted, and mixed in with flowing magma. These soften rocks come out with the volcanic eruption. Then, like I said in my other post, make their way to rivers, and collect sediment at the bottom forming the crystals inside.
    Whew…..that was a mouthful. Reply back if you need me to explain that in simpler terms……

  6. Janice says:

    Those geodes look really amazing. I read all of the comments and that sounds really interesting. The name geodes come from the word Geoides, the Greek word for earthlike. They are spherical and are comprised of a bunch of crystals. You really do learn something new everyday. πŸ™‚

  7. Janice says:

    Oh, also, please come and check out my blog at to comment on my blog and/or fill out my survey. Thank you! πŸ™‚

  8. me says:

    hey, i enjoyed reading about geode rocks. I wonder why they are called “GEODE ROCKS”? What do you think?

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