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Calcite Cone?
  
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John Betts




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PostPosted: May 16, 2019 11:03    Post subject: Calcite Cone?  

Does anybody recognize what this is and where it is from?

It is from the collection of Colorado collector Ruth Schwarz and was labeled as a "natural calcite cone" that was loaned for a club display probably about a specific mineral site. But no locality is given.

I suspect it is from Colorado...

It does fizz with HCL, so the calcite identification is probably correct.
Any help?



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Bergur_E_Sigurdarson




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PostPosted: May 16, 2019 11:27    Post subject: Re: Calcite Cone?  

Is the "cone" part referring to is being a fossilized plant-cone?

Looks cool :-)
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PostPosted: May 16, 2019 11:40    Post subject: Re: Calcite Cone?  

Quite probably the label is referring to a "Cone in Cone" sedimentary structure. You may take a look at the following Wikipedia page: https://en.wikipedia.org/wiki/Cone-in-cone_structures.
Or do some additional search through the internet.
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Peter Lemkin




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PostPosted: May 16, 2019 11:43    Post subject: Re: Calcite Cone?  

That definitely looks to me like a fossil cone that has been replaced by calcite or some similar carbonate. It doesn't look like a stalagmite or stalactite, the only other possibilities with such a shape.
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Kevin Schofield




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PostPosted: May 16, 2019 11:44    Post subject: Re: Calcite Cone?  

John Betts wrote:
Does anybody recognize what this is and where it is from?

It is from the collection of Colorado collector Ruth Schwarz and was labeled as a "natural calcite cone" that was loaned for a club display probably about a specific mineral site. But no locality is given.

I suspect it is from Colorado...

It does fizz with HCL, so the calcite identification is probably correct.
Any help?


Hi John...

The closest I can come up with is a piece of a "cone-in-cone" structure...although it is only really the bottom half-inch or so that has the vertically-striated structures that I would usually associate with the phenomenon.
Cone-in-cone is a rather poorly understood early diagenetic phenomenon wherein calcite (or aragonite, depending what you read) precipitates in mudrocks very shortly after deposition (or within tens to a hundred metres of the seabed), possibly in response to changes in the pH gradient. The conical form is a response to stress (or maybe an aragonite/calcite paragenesis...again, it depends which scholarly article you are reading).
Googling "cone-in-cone" will produce some pictures and lengthier expositions of how it forms...but nothing I have seen looks definitively like this one.
Locality could pretty much be AnyShale, Anywhere!

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PostPosted: May 16, 2019 11:46    Post subject: Re: Calcite Cone?  

Some how the above internet addres is not pointing back to the article that I wanted to share. Anyway, you can go straight into Wikipedia and search for the term or do it through Google, sorry.
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John Betts




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PostPosted: May 16, 2019 12:01    Post subject: Re: Calcite Cone?  

Yes, I am aware of cone-in-cone structures, and I already exhaustively searched the Internet. No luck.

I was hoping someone here would have personal knowledge of a calcite formation perfect conical structure and suggest a locality.

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Tom Tucker




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PostPosted: May 16, 2019 12:18    Post subject: Re: Calcite Cone?  

This does not look like the "classic" "cone-in cone" structures associated with impact structures, i.e., Crooked Creek, Missouri, but more resembles the similar forms I've seen surrounding large septarian concretions in Cretaceous age shales , as in Montana and Colorado.
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PostPosted: May 16, 2019 12:25    Post subject: Re: Calcite Cone?  

Tom Tucker wrote:
This does not look like the "classic" "cone-in cone" structures associated with impact structures, i.e., Crooked Creek, Missouri, but more resembles the similar forms I've seen surrounding large septarian concretions in Cretaceous age shales , as in Montana and Colorado.


Tom, I agree with you. My first thought was a septarian-like appearance when I view the conical surfaces under magnification.

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marco campos-venuti




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PostPosted: May 16, 2019 12:39    Post subject: Re: Calcite Cone?  

Hi, for me this is a classic cone-in-cone concretion. No calcite inside, but sediment of shale type.
I have many from different country and they looks all little different. They are diagenetic structures formed in large quantity in specific beds.
You can have pictures of a bed that can be a reasonably possible source at:
https(://)serc.carleton(.)edu/NAGTWorkshops/sedimentary/images/cone(.)html
Pictures are taken by Professor Dr. Diane M. Burns from Eastern Illinois University.
I suggest to write an email to her asking where she take the pictures.
dmburns(at)eiu(.)edu



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John Betts




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PostPosted: May 16, 2019 12:44    Post subject: Re: Calcite Cone?  

marco campos-venuti wrote:
Hi, for me this is a classic cone-in-cone concretion. No calcite inside, but sediment of shale type.


It is definitely composed of calcite.
One friend commented that he has seen these specimens before in collections from Colorado.

Please note it is a perfect cone, all around.

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marco campos-venuti




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PostPosted: May 16, 2019 13:25    Post subject: Re: Calcite Cone?  

Yes John, the inner portion of the structure is a perfect cone that you can pick up from the host rock.
I found in the web a deposit with similar color and shape of cones: DeQueen Limestone of the Gulf Coastal Plain of southern Arkansas. You can google it for more info.
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PostPosted: May 16, 2019 13:37    Post subject: Re: Calcite Cone?  

If you search in Scholar Google for "cone-in-cone structure, Colorado", there are many example from that state.
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PostPosted: May 16, 2019 15:18    Post subject: Re: Calcite Cone?  

Ed Raines at the Colorado School of Mines has seen similar from Fort Collins area and from east of Colorado Springs.

Case Closed.

Thanks everyone for your help.

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Pete Richards
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PostPosted: May 16, 2019 15:21    Post subject: Re: Calcite Cone?  

Apparently there is a cone-in-cone structure related to impact structures and one associated with large concretipns (Tom's post) but there is also a sedimentary structure in normal sedimentary rock sequences, which this looks very much like. The cones generally point both up and down within a stratum somewhat thicker than they are tall, and the stratum can persist laterally for hundreds of meters or more. I think they're supposed to have something to do with sediment compaction by de-watering during early diagenesis. They are sedimentary structures, not fossils. Because they form in and from sediments, they may have more or less calcium carbonate associated with them. The ones that I am familiar with are siltstone, and the calcium carbonate content is probably very small.
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PostPosted: May 16, 2019 15:41    Post subject: Re: Calcite Cone?  

Pete Richards wrote:
Apparently there is a cone-in-cone structure related to impact structures and one associated with large concretipns (Tom's post) but there is also a sedimentary structure in normal sedimentary rock sequences, which this looks very much like. The cones generally point both up and down within a stratum somewhat thicker than they are tall, and the stratum can persist laterally for hundreds of meters or more. I think they're supposed to have something to do with sediment compaction by de-watering during early diagenesis. They are sedimentary structures, not fossils. Because they form in and from sediments, they may have more or less calcium carbonate associated with them. The ones that I am familiar with are siltstone, and the calcium carbonate content is probably very small.


helluvan echo in here :-)

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