Lone Hunter Posted September 23, 2022 Share Posted September 23, 2022 (edited) 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. Edited September 23, 2022 by Lone Hunter 3 Link to post Share on other sites
Rockwood Posted September 23, 2022 Share Posted September 23, 2022 #3 looks like a septarian concretion with the dial set all the way toward septarian. 1 1 Link to post Share on other sites
Rockwood Posted September 23, 2022 Share Posted September 23, 2022 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 ? Link to post Share on other sites
Lone Hunter Posted September 24, 2022 Author Share Posted September 24, 2022 Hadn't thought of that, I suppose it's possible and would explain shape, since this isn't calcite what could the composition be? Link to post Share on other sites
Rockwood Posted September 24, 2022 Share Posted September 24, 2022 (edited) I think gypsum takes this form sometimes. And it is on the cursed list of some paleontologists for its distorted preservation. Edited September 24, 2022 by Rockwood 1 1 Link to post Share on other sites
Coco Posted September 24, 2022 Share Posted September 24, 2022 Hi, If it’s gypsum, you have to be able to scratch it with your nail. Coco Link to post Share on other sites
Lone Hunter Posted September 24, 2022 Author Share Posted September 24, 2022 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.' Link to post Share on other sites
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