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Volcanic rock that rattles

  1. Dec 12, 2016 #1
    I have a rock that I found while on a college class outing in Eastern Oregon. It is hollow inside and has multiple objects inside that rattle. I was told by a professor that isn't was formed when lava was ejected into the air and as it fell, it sort of ballooned out and solidified with smaller rocks inside of it. I have searched the internet and not found anything that fits this description. My guess is that it is a geode but it doesn't seem to match any of the descriptions or photos I have found. Can anyone tell me what it is?

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  3. Dec 12, 2016 #2
    Are you going to crack it open? :)
  4. Dec 12, 2016 #3
    I would rather not.
  5. Dec 12, 2016 #4


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    Seriously, online, looking at a picture, do you expect us to say what's inside? I have a rock that looks like marble on the outside, I've posted pictures, but the "marble" is striated across something visible inside, there are openings between the strings of "marble" like streaks. You can see another object encased inside of this marble like rock. Never seen anything like it, neither has anyone else. I love cool things like this.

    If you do decide to open it let us know. You might want to take it to a University's geology department and see if they have any way of looking inside of it, even if to bore a small hole and insert a camera.
  6. Dec 12, 2016 #5

    jim mcnamara

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    Looks like it could be pumicite - if it floats in water it probably is.
  7. Dec 12, 2016 #6
    Thanks for the replies. No, it doesn't float. I didn't expect anyone to know, I was just hoping. Does the explanation given by my professor sound reasonable? We found 7 or 8 of them on our trip.
  8. Dec 12, 2016 #7


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    Hi ya Bryon
    welcome to PF :smile:

    "rattle stones" ... have had lots of fun hunting for and finding the occasional ones of them when I lived in New Zealand ... there is also a sedimentary variety
    your profs' explanation is quite reasonable

    no, not really geodes, ( in the strictest definition) they form by a different mechanism ... in a mineral rich rock and water environment
    and they are usually quite spherical inside and out

    Basalt will often have cavities ... irregular in shape and filled with crystals of minerals such as Heulandite, Natrolite and a few other types of zeolites

    Last edited: Dec 12, 2016
  9. Dec 12, 2016 #8
    Awesome! Thanks for the info Dave!
  10. Dec 12, 2016 #9


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    Sounds like a hollow version of our state rock: Thunderegg

    Of course, without opening it, you'll never know.
  11. Dec 12, 2016 #10
    There are a few geodes in eastern Oregon, Idaho and Utah that rattle. It's possible that there are stones inside yours, but some rattlers that have been cut open also have poorly formed quartz crystals that possibly broke off.
    Smaller geodes tend to be spheroidal and are more typically picked up because they are small. We found several long, bomb-shaped rocks in Nevada a few years ago. One, about 42-inches long and 16 inches wide turned out to have a 34"x 12" crystal filling, mostly amethyst. Three were duds and one was cut in half before cutting it lengthwise. That rock was a geode, but not too impressive.
    If you ever do cut your rattler open, I would be interested in knowing what caused the rattling.
  12. Dec 13, 2016 #11
    This is all great information. Thanks for everyone's help. My curiosity is almost enough to make me cut it open but having a rock that rattles isn't very common. It is the only one I have left so I think I will keep it whole.
  13. Dec 13, 2016 #12
  14. Dec 13, 2016 #13


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