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Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?
  
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Troy Jr.




Joined: 13 Apr 2019
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PostPosted: Apr 13, 2019 14:12    Post subject: Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?  

Hi All,
I found this Travertine rock while fossil hunting an outcrop that is a Pennsylvanian era aquatic fossil bed. These types of specimens seem to be found mainly at the base of the hill/outcrop. This is the only one that you can see the orange and purple rust discoloration. This seems to be why there is orange, white, and smoky Calcite. Please feel free to comment or give input for correctness.
Thanks,



IMG_20190413_111108896.jpg
 Mineral: Calcite
 Locality:
Nebraska, USA
 Dimensions: 30 mm
 Description:
 Viewed:  462 Time(s)

IMG_20190413_111108896.jpg



Screenshot_20190413-131910.jpg
 Mineral: Calcite
 Locality:
Nebraska, USA
 Dimensions: 15 mm
 Description:
 Viewed:  468 Time(s)

Screenshot_20190413-131910.jpg



IMG_20190413_111811331_BURST000_COVER_TOP.jpg
 Mineral: Travertine
 Locality:
Nebraska, USA
 Dimensions: 75 mm
 Description:
 Viewed:  466 Time(s)

IMG_20190413_111811331_BURST000_COVER_TOP.jpg


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Kevin Conroy




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PostPosted: Apr 13, 2019 19:10    Post subject: Re: Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?  

The rust colored crystals in the second and third photos may be quartz. To test place a drop or two of vinegar on the crystals. If they are a carbonate mineral, such as calcite, you should see some bubbles form. No bubbles, probably quartz.

You can test the white massive mineral the same way. It's quite possible that calcite formed over the quartz.
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Bob Harman




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PostPosted: Apr 13, 2019 19:57    Post subject: Re: Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?  

Basically as Kevin says. The rusty stained areas are probably iron stained druzy quartz crystal tips while the blackish area are probably manganese oxide stained areas (wad). There may be some calcite (test with vinegar or acid for fizzing), but I don't see any definite calcite in your pix.

What makes you think the basic rock is travertine? I just see a piece of rock, NOS. Bob
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Dale Hallmark




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PostPosted: Apr 13, 2019 20:25    Post subject: Re: Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?  

Nebraska is predominately sedimentary geology. Although it does overlay crystalline rocks. And there is some uranium. Not impossible by any means but I would be surprised with Quartz other than nodules.

Dale
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Bob Harman




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PostPosted: Apr 13, 2019 21:10    Post subject: Re: Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?  

Not exactly what you are saying Dale, but druzy quartz crystal tips are found all over the sedimentary areas of the Midwest in both vugs and geodes. While the poster's example might be calcite, in Nebraska, druzy quartz is commonly found in the Southeast part of the state, in Gage county, also both in geodes and small vugs. Bob
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Dale Hallmark




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PostPosted: Apr 13, 2019 21:25    Post subject: Re: Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?  

Did not know that. I never suspected a Pennsylvanian era aquatic fossil bed might have quartz crystals. But then again most of my experience with fossils have been from Cretaceous limestone and marl.

Dale
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Troy Jr.




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PostPosted: Apr 14, 2019 08:28    Post subject: Re: Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?  

Here is some more info:
Specimens come from Nemaha Co., NE. Decades ago this location was a target for limestone extraction and they didn't take it all. Did some tests awhile ago. Vinegar test on a similar but separate specimen was positive for some Calcium Carbonate also sanded some down with a diamond belt. The main rock is marble hard. The specimen of interest that's pictured; UV light showed no sulfur absorption in crystals. Seems that this leached out of the nutrient rich sediment and hardened like it was in a cave.
Added some more pictures of from different angles.



IMG_20190413_111213755.jpg
 Mineral: Calcium Carbonate
 Locality:
Nebraska, USA
 Dimensions: 75 mm
 Description:
 Viewed:  309 Time(s)

IMG_20190413_111213755.jpg



IMG_20190413_111607732.jpg
 Mineral: Muscovite
 Locality:
Nebraska, USA
 Dimensions: 15 mm
 Description:
 Viewed:  307 Time(s)

IMG_20190413_111607732.jpg


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Susan Robinson




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PostPosted: Apr 14, 2019 11:56    Post subject: Re: Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?  

You won't find muscovite in a sedimentary environment. The thin plates that are in parallel growth are most likely weathered calcite.
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Bob Harman




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PostPosted: Apr 14, 2019 12:24    Post subject: Re: Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?  

There is only so much you can do with photos and limited testing on a rock such as you show.
I see iron and (probably) manganese stained quartz (?), probably calcite, and maybe some gypsum, all quite corroded, but found in the sedimentary environment of Nebraska.

I don't see anything that I might call travertine. As Susan notes, Muscovite (mica) essentially has nothing to do with Nebraska's sedimentary rocks.

Bottom line for me is that you should look to join a local rock club or society where experienced folks with similar interests to yours will be of help teaching you Nebraska's mineralogy and geology. Bob
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Troy Jr.




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PostPosted: Apr 14, 2019 13:59    Post subject: Re: Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?  

Susan Robinson wrote:
You won't find muscovite in a sedimentary environment. The thin plates that are in parallel growth are most likely weathered calcite.


Thanks for the info, very helpful! Susan, After I posted and zoomed in the picture you're commenting on, I began thinking the same thing and Muscovite makes no sense. Our expeditions in SE Nebraska are proving to be very challenging with identification of everything. USGS has this area listed as mostly unexplored. Being on the Nemaha uplift the surface can be very diverse, then throw in glacial till and it makes it a 3D crystal puzzle(pun intended). Had recent success identifying a unique Iron-Cemented Dakota Sandstone loaded with mineral. It was so difficult it had to be identified through a University channel who had to consult her colleagues. My son and I were very grateful. Thanks, again.
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Troy Jr.




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PostPosted: Apr 14, 2019 14:07    Post subject: Re: Nebraska Travertine with small multi-color Calcite. Maybe some macro Muscovite?  

Bob Harman wrote:
There is only so much you can do with photos and limited testing on a rock such as you show.
I see iron and (probably) manganese stained quartz (?), probably calcite, and maybe some gypsum, all quite corroded, but found in the sedimentary environment of Nebraska.

I don't see anything that I might call travertine. As Susan notes, Muscovite (mica) essentially has nothing to do with Nebraska's sedimentary rocks.

Bottom line for me is that you should look to join a local rock club or society where experienced folks with similar interests to yours will be of help teaching you Nebraska's mineralogy and geology. BOB


HaHa Bob; Bottom Line: How to Identify Rocks: Find Friends

MARBLE is metamorphosed limestone or dolomite. The colors can vary from pure white to gray, green, yellow, brown, black, red or any combination thereof, depending on the ‘impurities’ in the parent limestone. Bands or streaks result from plastic flow during extreme deformation, due to high pressure and temperature.

It is calcite or dolomite and will fizz in weak acids. "Retrieved From,"(Susan Celestian – Curator of the Arizona Mining and Mineral Museum. Stan Celestian – Photographer and Instructor).

Also wanted to add Bob, that there is Granite everywhere in this area, and if I remember it is composed of:
1) quartz
2) feldspar
3) MICA
4) hornblende.
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