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

[Mikeinri 0]

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

Edited March 1, 2016 by Mikeinri

[Au Seeker 3,153]

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

[Mikeinri 0]

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?

[Au Seeker 3,153]

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.

[d_day 341]

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?

[Mikeinri 0]

They are same on borh sides. None seem exactly the same.

[Mikeinri 0]

Maybe not exact on both sides. Can kind of see where it would have been laying on the ground, not as deep cracks but still there and not much of a difference.

Edited March 1, 2016 by Mikeinri

[Mikeinri 0]

Pics of bottom and top

[4meter 200]

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

[Mikeinri 0]

They are so small compared to what I see online. Also many look much more colorful and even color in the stone.

[d_day 341]

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.

[d_day 341]

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.

[Mikeinri 0]

I have now broken one in half.

[Mikeinri 0]

And should I have not broken this?

[Au Seeker 3,153]

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.

[Mikeinri 0]

Thank you all for your expertise!