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Thread: What sort of rock is this?

  1. #1 What sort of rock is this? 
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    What am I looking at here exactly?

    My first guess was just common chert. Then I thought that it may be limestone, given the texture of the bit of gray area. I red that Limestone can have impurities to make it red in some areas. But it's like the texture changes where the color changes. The gray is rough while the brown/red areas are a bit more smooth. I took it in to my science professor and he said he really wasn't sure where to begin looking either. He said the closest thing he could relate it to was jasper which, when he showed me a piece, does seem to resemble the brown areas on what I'm showing below.

    My best guess is still that it's just limestone, but I'm not extremely knowledgeable in this area. Anyone else know, or at least have better ideas?







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  3. #2  
    Time Lord Paleoichneum's Avatar
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    Do you have any information on where the rock if from, and what the local geology is?

    Also clearer pictures and closeups are needed to get any ideas.


    If more of us valued food and cheer and song above hoarded gold, it would be a merrier world. -Thorin Oakenshield

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  4. #3 Rock key 
    Forum Freshman dinky's Avatar
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    PCMoon, Hi, you may find the rock key at the following link helpful.
    Rock Key
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  5. #4  
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    It does not look like lime stone to me
    Limestone will react with vinagar.
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  6. #5  
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    The grey area's texture reminds me of wacke.

    EDIT: Actually, I might be on to something. I read that wacke is a loosely held together sandstone within a clay matrix. Maybe that would explain the redish brown areas?
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  7. #6  
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    Quote Originally Posted by PCMoon View Post
    The grey area's texture reminds me of wacke.

    EDIT: Actually, I might be on to something. I read that wacke is a loosely held together sandstone within a clay matrix. Maybe that would explain the redish brown areas?
    As Sealeaf suggests, find out if it evolves bubbles when vinegar is dropped on it, for a start. Then we can rule in or out CaCO3 in its various manifestations.
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  8. #7  
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    It does nothing when immersed in vinegar.

    It is from Alabama which would probably suggest the redness, if my understanding is correct in thinking it may be clay.
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  9. #8  
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    Quote Originally Posted by PCMoon View Post
    It does nothing when immersed in vinegar.

    It is from Alabama which would probably suggest the redness, if my understanding is correct in thinking it may be clay.
    OK so not limestone etc. What is the geology of Alabama? Where exactly did it come from?
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  10. #9  
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by PCMoon View Post
    It does nothing when immersed in vinegar.

    It is from Alabama which would probably suggest the redness, if my understanding is correct in thinking it may be clay.
    OK so not limestone etc. What is the geology of Alabama? Where exactly did it come from?
    I got it from a wall of rocks behind my house. But I do think the rocks came from within Alabama. The southeast (Alabama in particular) is known for its very red, and very rocky soil.
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  11. #10  
    Time Lord Paleoichneum's Avatar
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    Most of the southern portion of Alabama is alluvial deposits from further north.
    If more of us valued food and cheer and song above hoarded gold, it would be a merrier world. -Thorin Oakenshield

    The needs of the many outweigh the need of the few - Spock of Vulcan & Sentinel Prime of Cybertron ---proof that "the needs" are in the eye of the beholder.
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  12. #11  
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    Quote Originally Posted by Paleoichneum View Post
    Most of the southern portion of Alabama is alluvial deposits from further north.
    The first thing that came to my mind when looking at your pic was 'kyanite' .....then again, my eyes are not that great and I may be way off base. The brittle texture and bladed shape of the crystals tends to 'give away' kyanite, but more amorphous (less well formed) varieties are more challenging to discern. I am familiar with the blue version but I note that it does occur in pink varieties as well. Kyanite (an alumino-silicate) is usually associated with fairly intense metamorphism associated with granitic intrusions in prior marine based lithology. Some varieties, particularly with well-defined crystallography are very attractive. :-))
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  13. #12  
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    Very clearly no Kyanite. It doesn't show the basal or terminal cleavage, or the fibrous crystaline structuring.
    If more of us valued food and cheer and song above hoarded gold, it would be a merrier world. -Thorin Oakenshield

    The needs of the many outweigh the need of the few - Spock of Vulcan & Sentinel Prime of Cybertron ---proof that "the needs" are in the eye of the beholder.
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  14. #13  
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    Quote Originally Posted by Paleoichneum View Post
    Very clearly no Kyanite. It doesn't show the basal or terminal cleavage, or the fibrous crystaline structuring.
    Cheers :-))
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