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How did you clean it?

@patrick-hsieh read the discription

I cleaned it first using a micro-sandblaster with a soft media and low air pressure, then used an ultrasonic cleaner.

the possibility of it being a crystalised crinoid is tantalising, but l’m not sure we can confirm with certainty if it’s one or not. the evidence is still quite ambiguous.

Thanks for the reply @Leonardo-Miranda. I appreciate your input

I had one from Southern Indiana years ago that was most certainly a crinoid. Love those sedimentary geodes!

Thanks for the tag, @a-trilobite, I wasn’t aware I was tagged in the description. The picture provided is from an oblique angle, which makes it difficult to tell if there is any radial symmetry. For example, a picture looking down the specimen from what you’ve labeled as the calyx and another picture looking straight down from the other end would be helpful. From your picture, the putative arms do not appear identical or even the same size as each other, which you would expect. One of the things I look for on the calyx are the plates which are important for identifying the crinoids. I don’t see any of those as well. I suppose its possible the crystallization process has progressed so far as to obliterate those as well as distorting the arms but so far there isn’t enough evidence to suggest a fossil.