Stromatolite? Help with ID, please...

[Miket]

Found this in Western South Dakota, someone suggested it might be Stromatolites?  Anyone know?

Thanks!

 

[GeschWhat]

Welcome to the forum. I don't know what it is, but I'm sure someone here will. Very interesting! 

[DPS Ammonite]

Welcome to the Fossil Forum.

 

It is not a stromatolite since they are solid layered structures that are not likely to fall apart and create the little bits and pieces that you see. 

 

Where is the rock from?  A specific locality will help with ID. Are the white areas calcite or quartz?

 

A good guess based on overall folded "cornflake" shape: Phylloid algae.

 

http://www.lakeneosho.org/King1Pic157-Tech.html

 

https://en.m.wikipedia.org/wiki/Stromatolite

 

 

[Miket]

I'll try to get a better picture, I believe the white areas are calcite- I'm fairly new to all of this so I'm not really sure.  I do know that it isn't quartz.  I found it in Fairburn, SD, actually.  Out looking for Fairburn Agates and it caught my eye.  As can be seen from the photos, the top part is raised and very textured, it's super interesting...

I'll also research the Phylloid algae, thanks!

[abyssunder]

It reminds me of Coquina . (Coquina jasper/agate ?)

[Tidgy's Dad]

Hello, Mike, and a very warm welcome to TFF from Morocco! 

Looks like mineral banding to me.. 

if it's not part of the famous agates from around that area then some calcitic layering or it may be coquina as abyssunder suggests. 

[ashcraft]

You can test for calcite by dropping vinegar on it.  Calcite will fix.

 

Brent Ashcraft

[ynot]

3 hours ago, ashcraft said:

Calcite will fix.

Calcite will fizz.

Can You scratch it with a knife?

[FranzBernhard]

This one sprang immediately to my mind, coquina made of congeria bivalves from Fohnsdorf, Styria, Austria (Carpatium). Wide of polished specimen 14 cm.

(Just for comparision and to show off a nice local fossil-rock ).

Franz Bernhard

[Miket]

That does look similar, I haven't had a chance to try vinegar or a scratch test yet...

[DPS Ammonite]

1 hour ago, FranzBernhard said:

This one sprang immediately to my mind, coquina made of congeria bivalves from Fohnsdorf, Styria, Austria (Carpatium). Wide of polished specimen 14 cm.

(Just for comparision and to show off a nice local fossil-rock ).

Franz Bernhard

@FranzBernhard  Franz, I think that you have a very interesting rock (much more interesting than a coquina) and would love to know more about it. I am having a hard time seeing the shells since you call it a coquina. I find it hard to understand how shells could be folded into S shaped folds without breaking into pieces. I think that it looks like a layered rock (shale and carbonate?) that was deformed before the layers were lithified. It is also known as soft sediment deformation.

 

See: https://www.sciencedirect.com/science/article/pii/S2095383616300530

[abyssunder]

for comparison: Coquina jasper

 

[FranzBernhard]

@DPS Ammonite, I don´t unterstand it, too! In my picture, the S-shaped forms are made of carbonate, some black parts in beween are shale or coal. Google for "Fohnsdorfer Muschelkalk", you will find a specimen with more (carbonatic) matrix. Matrix can be shaley or carbonatic, the rock forms an up to 3 m thick layer immediately above a thick subbituminous coal seam and was used as building stone. Very rarely, you can find thin coal layers betweeen the shell layers (unfortunately not a very good photo, wide of specimen ca. 7 cm).

 

Addition: Here is a paper about the area, unfortunately in german:

http://www.sediment.uni-goettingen.de/staff/dunkl/zips/Sachsenhofer-et-al-2010.pdf

For the rock in question, see pages 32 and 34.

Franz Bernhard

[supertramp]

What’s the size of the specimen?

It resembles some of the so many “marble” known in Italy as “lumachella”, which actually are bioclastic limestones; 
don’t know if it corresponds to the spanish coquina

 

https://www.google.it/search?q=lumachella+ancient+rome&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjgksCvhorbAhVFWxQKHb-wA5cQ_AUICigB&biw=1517&bih=707#imgrc=DU4PqSBZUgFxvM:

 

ciao