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Can someone help identify this rock if it is indeed a rock


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Not sure if this was made this way from a river/stream eroding the rock or maybe from fossils in bottom of lake or if it is perhaps not even a rock but a mold and some other material? Any help to solve this mystery for me would be appreciated! Thank you in advance

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Edited by Mikeinri
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Very interesting, I hope someone knows what they are, a little for info would help in IDing these, tell us in general more of where/what part of the country they were found and in what type of environment

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They were found in an auction in north eastern Connecticut. Usa. I like to collect natural sharpening stones/ razor hones and these were not much money so purchased because I guess I like rocks.. Wasn't sure they were not man made for an aquarium or something or natural. Wonder if breaking one would help?

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You can do a streak test, hardness test which could help, but breaking one is up to you, don't know if it would help with IDing these or not,

If they're man-made, especially using a mold I would think that you would have at least some duplicates that are exactly the same, especially if you have more than what you show in your photo.

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Strictly a guess here, but I'm thinking some kind of mudstone. I imagine them drying and cracking slowly over time. I would expect these formed similar to the way a septarian nodule forms, but from the outside rather than inside. Are the apparent cracks equally pronounced on both sides?

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Mikeinri, those are "Septarian Nodules"; very nice ones. Here is link to some info on Setarian Nodules

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There's another possibility that just occurred to me. These might be coprolites. Most coprolites don't resemble these at all, but a handful do. Taking them to a local university's geology department should get you some more definitive answers.

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Also, the less pronounced cracking on the undersides is about what I would expect to see for something that dried and cracked on the open air. It still doesn't mean I'm correct, just that that's what I expected.

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After seeing the inside of the one you broke, I agree with 4meter that they are Septarian Nodules which have the inside voids from cracking filled over time with Calcite which the broken one appears to have.

I don't think they're very valuable so breaking the one shouldn't be a great loss.

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