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The image below was taken on a hike. Circular patterns at bottom (it is flatter on this face and round otherwise) appear either man-made or possibly it is a fossil.

Any idea what this could be?

Rock of interest:

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  • $\begingroup$ Welcome to Earth Science StackExchange! Could you provide a bit more information? Please follow this guide: meta.earthscience.stackexchange.com/a/125/56. $\endgroup$ – arkaia Jan 17 '17 at 18:42
  • $\begingroup$ I don't suppose you have a picture of the chipped side. It's useful to see an unweathered surface when identifying rocks $\endgroup$ – haresfur Jan 17 '17 at 22:59
  • $\begingroup$ There look to be some radial markings in the centre which lead me to suspect that this is a fossil but I'm no expert on what it could be. $\endgroup$ – bon Jan 18 '17 at 8:09
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    $\begingroup$ OTOH From this single photo with lack of information, this could be concrete $\endgroup$ – Jan Doggen Jan 18 '17 at 10:59
  • $\begingroup$ It could be a concretion having a image of the other side and the broken surface would help a lot. Density and were it was found will help as well. If the other side is broken off you might have a fossil or at least a cast of one. $\endgroup$ – John Jan 18 '17 at 15:29
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The face of the rock with the round center portion looks strongly like a Rugosa or Horn Coral. I suggest it is a Rugosa coral because of the center with the radial lines out from the center and the clear edge surrounding the radial lines. See https://en.wikipedia.org/wiki/Rugosa.

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  • $\begingroup$ Thanks for the feedback. The distinct feature that made me suspect fossil was the radial lines out from the center as well, in which case Rugosa makes sense. $\endgroup$ – DrTarr Jan 19 '17 at 1:08

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