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Specimen with screw-like object inside
  
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Jennifer King




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PostPosted: Jun 17, 2017 23:55    Post subject: Specimen with screw-like object inside  

This rock appears to have a screw inside. My son found it near a lake in Greene County, MO. He showed me some outrageous on-line stories about similar findings. Is this anything special? What kind of rock is this? Any idea what this object inside is? Is it organic?


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kushmeja




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PostPosted: Jun 18, 2017 00:13    Post subject: Re: Specimen with screw-like object inside  

If it is indeed natural, then it's probably a crinoid fossil, or something similar in limestone. Crinoid ate worm-like and create fossils that look like cylinders with rings. It's hard to tell from the pic though.
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alfredo
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PostPosted: Jun 18, 2017 00:34    Post subject: Re: Specimen with screw-like object inside  

I agree that it looks like a crinoid fossil. Interesting find!
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marco campos-venuti




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PostPosted: Jun 18, 2017 03:25    Post subject: Re: Specimen with screw-like object inside  

It is the internal cast of a piece of a crinoid stem. They are quite common fossils. But this is not the right forum.
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Bob Harman




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PostPosted: Jun 18, 2017 04:57    Post subject: Re: Specimen with screw-like object inside  

YEP!! A segment of crinoid stem. Quite common in the sedimentary regions of the Midwest.

Crinoids, commonly called sea lilies, were common in the Mississippian age. They were animals, many species of which had long stems, up to 20' in length. Their heads looked like lilies, waving in the nutrient rich shallow waters grabbing whatever washed past them.
Some of the very best fossil examples come from Crawfordsville Indiana. Check out their pix on line. BOB
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alfredo
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PostPosted: Jun 18, 2017 05:19    Post subject: Re: Specimen with screw-like object inside  

I like this one because it appears to sit in a hollow vug. The crinoid bits I've seen before were all embedded in solid rock, or else loose with no matrix. Probably no big deal to those of you living in the fossiliferous Midwest, but to me, living surrounded by igneous rocks and not a fossil in sight anywhere, it looks interesting ;))
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alanbartlett




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PostPosted: Jun 18, 2017 09:35    Post subject: Re: Specimen with screw-like object inside  

Almost identical to one I found in a now filled in sand/gravel quarry 1/2 a mile from home in Worksop, Nottinghamshire, UK - a few thousand miles from you though!
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James
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PostPosted: Jun 18, 2017 11:41    Post subject: Re: Specimen with screw-like object inside  

I have one that has Blue John fluorite on it.

James
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Pete Richards
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PostPosted: Jun 18, 2017 11:45    Post subject: Re: Specimen with screw-like object inside  

alfredo wrote:
I like this one because it appears to sit in a hollow vug. The crinoid bits I've seen before were all embedded in solid rock, or else loose with no matrix. Probably no big deal to those of you living in the fossiliferous Midwest, but to me, living surrounded by igneous rocks and not a fossil in sight anywhere, it looks interesting ;))


This is a mold of the crinoid stem fragment, which had a nearly cylindrical outer surface and a screw-like hole (actually ribbed, not a screw) down the middle. The crinoid fossil material was surrounded by and the hole filled with fine sediment of some kind, then the carbonate fossil material dissolved away, leaving what we see now.

An interesting fact: crinoid fossils are made up of many plates, but each plate is a single crystal of calcite!

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Collecting and studying crystals with interesting habits, twinning, and epitaxy
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alfredo
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PostPosted: Jun 18, 2017 18:29    Post subject: Re: Specimen with screw-like object inside  

Thanks for the explanation, Pete!
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Peter Perkins




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PostPosted: Jul 09, 2017 14:48    Post subject: Re: Specimen with screw-like object inside  

I've been away and only just seen this topic.I think one stage has been missed out - I think the fine sediment Peter mentioned would have been calcite mud. Then in a later stage of lithification the calcite mudstone, but not the calcite stem fragment, was silicified. Then, later, the crinoid stem fragment was removed, probably by solution leaving a hollow where the fossil had been.
Peter
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