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I've been picking up rockhounding again and recently found a neat rock on the Mississippi River around St. Louis, Missouri during this drought. After finding some recent chipped fragments of a larger boulder and taking them home, the patterning makes me think this might be more than just some beautiful banding -- perhaps algae, coral, or other? The regular nature of the banding and the perpendicular pitting/weathering is making me think it could be more than meets the amateur eye. Unfortunately, this boulder was dumped on the river, so I have little knowledge of what formation it is from. Most of the nearby rocks seem to be Mississippian limestone, but this is isn't limestone. Part of the longest photographed rock was exposed above the sand & clay when it was underwater, thus sandblasted smooth. The rock reacts a bit with vinegar, but not vigorously. The background mat is marking 1 in squares, and the ruler in the side of some photos is cm. Photos with circular black areas are taken through a 10x loupe attached to my phone. Please let me know if you want more photos of anything specific. The rightmost piece & last photo are the newly expose face that was chipped off when I found it. Advice for anyone reading this: Never step foot in the Mississippi River, and profusely clean anything you collected from the river. It is a dangerous and horrifically polluted river.

I see banding on the edges, so is it an agate? I cut it in half and it has a purple inside. Is that amethyst?

I've been working through a number of Green River fish I caught from the split fish layer (now called the sandwich layer) at the Warfield Fossil Quarry about 10 years ago. They have been stored away and I'm just now cleaning them up for display. Here are two slabs that are the part and counterpart of a Knightia eocaena. I split it out at the quarry, brought both halves home, sawed them into two rectangular slabs, then wrapped them up individually in two sheets of bubble wrap and put them away for all those years. After pulling them out of storage today and running some water over them to wash off the dust, I noticed this strange purplish-blue band running diagonally through the fish. It has very sharply defined edges and runs all the way through both slabs (you can see it on the sides and backs of both slabs). I've never seen anything like this before. Does anyone have any ideas what might have caused it?