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KimTexan

Septarian nodule?

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KimTexan

I found the coolest rock I may have ever found today while out hunting for fossils. I hit the mother load on the fossils, but the rock is absolutely more fascinating at this point. More on the fossils later.

I think the rock is a fragment of a septarian nodule that seems to be comprised almost entirely of what I believe may be aragonite and maybe a tiny bit of calcite.

I found it in Post Oak Creek practically in the Sherman city limits. The formation in the creek is Alluvium which is Quaternary, Holocene, Cenozoic (in reverse order) I believe. It is surrounded by Austin chalk which is cretaceous.

Can anyone help confirm the identity or tell me otherwise? Also, can anyone educate me about septarian nodules of this nature in the Alluvium or do you think It came out of the Austin Chalk?

Any help our input is appreciated.

 

 

056AFFEC-1199-4D23-BAE6-73009729404C.jpeg.d2e863d01eca2f744cbf2e9e5876e8e9.jpegClose up so you can see the crystle color and crystal form. Is it araganite? @ynot I know you’re a crystle/mineral guy. What do you think? Any idea how it formed?

I saw a different kind of septarian nodule last week at Fossilmania in Glen Rose that came from the Main Street formation in Dallas county that were formed around ammonites. These look pretty different than those though.046A0606-AF51-4C48-BE0C-F396710555C9.jpeg.265b3f34fdbb54355655cec1c09023a9.jpegI’d call this the top down look. Side 1 of 5. It looks a bit like a thin separating ridge or wall/fin like structure that is also aragonite looking or a brown crystal.69D27E37-2C45-445F-B7AE-2DA7693A2E33.jpeg.a600de80366a935ee10726995d8598a9.jpeg

Side 2. There are some kind of clear yellow crystals mixed with the brown with a different shape to them. There’s even some amber looking color in there. 365A8906-B3C9-4DAE-92EC-C29A7134F66E.jpeg.48a0e06d2a4752d412084f43bd5ebfc5.jpeg 

Side 3 

01E0FB42-245D-4A5D-B25F-1CBDD310F965.jpeg.f092e153581144b475d47ee63990d1c4.jpegSide 4

C0214E5F-7DD9-4DD3-9956-817BAA5D9BB7.jpeg.f75c5bc7596d6746369b0758557f85d4.jpeg

Side 5

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Nimravis

Very pretty.

 

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GeschWhat

Beautiful!

 

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DPS Ammonite

It is a septarian nodule from the Arcadia Park Formation and is composed of different colors of fluorescent calcite. See my nodule in the collections under pseudofossils. Eagle Ford Group septarian nodules usually fluoresce under both short and long wave UV light. Try it out.

 

P1020151.JPG.b2d73bbe1064437ec8e7704bace90e90.JPG

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ynot

It does look like part of a septarian nodule. 

The crystals are most likely calcite which can have many crystal shapes and colors in one piece.

DPS Ammonite beat Me to the post.

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abyssunder

Everything is in the septarian range, including the double-row pattern of the walls.

 

17584-17584.thumb.jpg.7fef0c6cdbca106d944f6d071e8e572c.jpg

excerpt from here

Edited by abyssunder

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KimTexan
On 11/4/2017 at 11:15 PM, DPS Ammonite said:

It is a septarian nodule from the Arcadia Park Formation. 

Where is the Arcadia Park Formation? I have not been collecting this far north in Texas until the past month or so and I had not started to learn my formations until then.

On 11/4/2017 at 11:15 PM, DPS Ammonite said:

 

P1020151.JPG.b2d73bbe1064437ec8e7704bace90e90.JPG

DPSAmmonite, that is absolutely beautiful, exquisite, gorgeous! I love it! :wub: I’m mesmerized by it. Wow! Soooo cool.

How big is it?

How hard are those to find? 

What formation was it in?

It looks like a one in a million kind of find. I will definitely try to find your nodules in the collection area and have a look. 

I have a black light flashlight somewhere. I moved a couple months ago and haven’t gotten everything unpacked yet.

 

I met a lady at Fossilmania who was selling septarian nodule fragments that formed around ammonites. They had yellow calcite and araganite in them. I think she said they came from Rockwall, in the Mainstreet formation. She said the nodules were about 90 pounds, but only 2 of ever 10 had anything inside of them. They were found during construction of some business. So there must be nodules in a number of places.

Did the Arcadia Park nodules form around any particular critter?

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DPS Ammonite

 

 

The nodule is about 9 inches across which is my favorite one that I found. They are locally common in the Eagle Ford. Some even have great crystals in them.

 

The Arcadia Park Formation (part of the Eagle Ford Group) is below the Austin Chalk/Atco Formations. The Eagle Ford crops out on the west side of Dallas: https://www.twdb.texas.gov/groundwater/aquifer/GAT/dallas.htm

 

Septarian nodules don't usually form around criters. However, fossils do occur in other types of nodules in the Eagle Ford. 

 

BTW the Mainstreet Formation does not occur near Rockwall, TX. Ozan and /or Austin Chalk occurs there see link to Dallas geology map above.

 

If you have not done so, check out the Dallas Paleontology Society. The are very helpful with ID's and will lead you to many new sites.

 

 

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PyritizeMe

Very unique , definitely looks like calcite . Try shining a ultraviolet light on it to determine its nature .

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