Fossil or rock

[Nanschut]

We found this in the upper peninsula of Michigan and can’t figure out what it is. Rock or fossil. Please see pictures

 

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[Oddjob]

No idea, but very cool looking.

 

[Nanschut]

The end is cool and it weighs 20 lbs

 

[Kray Gelder]

ROCK.

 

[Gaspipe]

Rock

 

[glenn37216]

It's an Alien egg ! .............................................................................................................(or a rock.)

 

[kingskid1611]

Large turd from a dinosaur.....

 

[Jarl]

It's weathered and appears to have some silicified material in the crevices(question is, what did it look like before being weathered?). You should scratch test different parts of the specimen to see what the hardnesses it has. At first glance, I'm leaning towards it being a rock. I don't think it's an igneous rock. I would guess it to be either sedimentary(the inside core mostly) or metamorphic but it seems that something enshrouded the core at a later time and then weathered away. The core appears to have been encased over time in layers...maybe by recession of water...maybe it was lodged or was stuck into something vertically(maybe inside a cavern or cave) full of water that slowly evaporated, collecting and forming layers around the core. If that isn't the case, then the specimen would have to have been formed as it is, minus weathering. What would cause that...or how would it occur? Don't know(sedimentary process??). It could also appear as it is...fine layers...as a result of weathering alone...say if it were a nice smooth rock at first then buried as glacial deposition or other...the mud or silt around it gradually being blown away by winds over time...forming layers of weathering.

I thought it resembled a shark coprolite a little, but that's probably not what it is. If it was a living thing, maybe it was a type of coral. The only other thing...off the top of my head to suggest is possibly a stromatilite or cyanobacteria.

 

[Jarl]

Then again...the default answer is generally...'a concretion'.