We found this in our back yard (in Michigan) while digging one day. I'm curious about it, it seems different than others we've found. It's a pretty good size, about the size of a basketball.enter image description here

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    $\begingroup$ Required reading: meta.earthscience.stackexchange.com/questions/124/… Then please update your question. $\endgroup$ – Jan Doggen Aug 5 '16 at 15:26
  • $\begingroup$ Could you break and show interior of the rock? also could you take zoom photo of inner and outer portion. For any natural-object, please give a scale. Not necessarily a metering-scale, you could provide a coin, or matchstick etc common object with known size (choose it according to zoom level) $\endgroup$ – Always Confused Aug 6 '16 at 18:25