Tiny black balls and unknown object

[Lone Hunter]

This particular piece of marl from Grayson caught my eye because of the little balls covering it then I saw the odd grooved chip, it's very thin and I'm not recognizing it as shell.  So what are these things?

[DPS Ammonite]

The ribbed piece looks like a Protocardia clam.

 

The black balls probable are pyrite/marcasite or their weathering products, assuming the balls are not soft algae or lichen.

 

See picture from northtexasfossils website.

http://northtexasfossils.com/clams.htm

Edited November 27, 2021 by DPS Ammonite

[digit]

Not sure if the same mineral taphonomy extends back to Cretaceous fossils but we quite frequently have Miocene fossils with small black (usually somewhat soft and powdery) crystals of manganese oxide. This is the same material that creates the manganese dendrite pseudofossils.

 

https://www.researchgate.net/figure/Examples-of-each-class-of-intensity-of-manganese-coatings-on-cave-bear-metapodials-as_fig1_223744099

 

https://woostergeologists.scotblogs.wooster.edu/2013/01/20/woosters-pseudofossil-of-the-week-manganese-dendrites-from-the-germany/

 

Cheers.

 

-Ken

[Lone Hunter]

These are very hard, feels like rubbing sandpaper.  Are all dendrites formed from manganese? I have a stone with reddish dendrites wondering if it is the same thing.

[abyssunder]

On 11/27/2021 at 9:38 PM, Lone Hunter said:

These are very hard, feels like rubbing sandpaper.  Are all dendrites formed from manganese? I have a stone with reddish dendrites wondering if it is the same thing.

Not all dendrites are manganese dendrites (the black ones). There are also iron-oxide dendrites (the reddish ones) for example on the Solnhofen plates. Sometimes both are present.