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A few odd Woodbine things


Lone Hunter

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All of these came from a cliff face on lake Grapevine,  no.1 both of these stood out because of rounded shape, plucked from the face of uppermost part of cliff. no.2 there was a thin layer of limonite running length of ledge, all was unremarkable I saw except this piece, thinking impression of plant material? no.3 assuming it's a concretion, thought it was an ammonite when it was cloaked in dirt, found in crevice with some gravels at top of cliff,  doesn't look like Woodbine material so stood out, not calcite. Pics are out of order, first one should be last.

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Edited by Lone Hunter
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#3 looks like a septarian concretion with the dial set all the way toward septarian. :)

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19 hours ago, Lone Hunter said:

no.3 assuming it's a concretion, thought it was an ammonite when it was cloaked in dirt

12 hours ago, Rockwood said:

#3 looks like a septarian concretion with the dial set all the way toward septarian. :)

 

Wouldn't such a concretion form in a void that repeatedly filled with ground water and dried ? And wouldn't this shape of void correspond well with a dissolved ammonite shell ? 

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Hadn't thought of that, I suppose it's possible and would explain shape,  since this isn't calcite what could the composition be?

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I think gypsum takes this form sometimes. 

And it is on the cursed list of some paleontologists for its distorted preservation.

Edited by Rockwood
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Yes I can scratch it with nail and it streaks white, pretty sure it's gypsum. Did additional test before that for calcite again after running across the following information on Mindat, I've always just plopped it in vinegar and looked and listened for fizz/bubbles.  Might explain a lot of non reactive things I thought were calcite and help others when it comes to doing the fizz test correctly.                     'With vinegar, you usually need to use a powder to see much effervescence: crush a little, or scratch the surface, put a few drops on and look under a hand lens for any bubbles.'

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