Just a rock, or a fossil bivalve?

[Joeinmorgancounty]

Happy new year. This is my first attempt at a post, so try and go easy. I respect the depth and breadth of knowledge in this forum. Thanks for yours in advance.

 

Unfortunately I do not have a proper provenance for this specimen. This peice was purchased at auction with a rock lot, silified chalcedony (agate), and I was surprised at the symmetry and shape. My amateur mind brought me to fossil bivalve. Another specimen from the same lot shows this exact shape and general size, so here I am. 

 

What are your thoughts? Thanks again.

 

125mm x 115mm x 60mm

1216g or 2lb 10oz

 

[FranzBernhard]

Welcome to TFF from Austria!

 

Color variation pattern and overall texture suggest chert/flint nodule.

Does it fizz with vinegar or hydrochloric/muriatic acid?

The abundant cm-sized, shallow pits could indicate, that this specimen has gone through a (wild)fire.

 

I don´t get any bivalve vibe.

 

Franz Bernhard

[Rockwood]

Do you suppose it could be a stone that was used to heat cooking pots ? An artifact.

[Joeinmorgancounty]

13 minutes ago, FranzBernhard said:

Welcome to TFF from Austria!

 

Color variation pattern and overall texture suggest chert/flint nodule.

Does it fizz with vinegar or hydrochloric/muriatic acid?

The abundant cm-sized, shallow pits could indicate, that this specimen has gone through a (wild)fire.

 

I don´t get any bivalve vibe.

 

Franz Bernhard

Thanks Franz. No reaction to vinegar. You are right, nodules are sometimes deceptively symmetrical,.

[Joeinmorgancounty]

6 minutes ago, Rockwood said:

Do you suppose it could be a stone that was used to heat cooking pots ? An artifact.

Are the pits on this piece we see usually do to heat flaking/pitting?

[Rockwood]

34 minutes ago, Joeinmorgancounty said:

Are the pits on this piece we see usually do to heat flaking/pitting?

The shapes seem right to me from seeing stones in a fire pit, but outside of that the closest I can claim to experience is having watched an old episode of Time Team. 

They heated stones and dropped them in water to make tea.

[Bob Saunders]

seeing that you are from Indiana and If from Indiana I would consider a Chalcedony geode.  Like from the Bloomington area. It may also have been heated a s a warming stone, like for the horse and buggy. 

[Ludwigia]

I'd go for something like chalcedony as well. Looks pretty weathered.

[Mark Kmiecik]

9 hours ago, FranzBernhard said:

The abundant cm-sized, shallow pits could indicate, that this specimen has gone through a (wild)fire.

I agree. Or multiple campfires as part of a firepit.

[grandpa]

Sure does look like some of the Keokuk Geodes I have in my collection from the Iowa/Illinois/Missouri Tri-State area.  I have some from that area that have similar coloration and botryoidal chalcedony structure.  I even think I see some gaps in the surface with dark crystals inside.  It's a beautifully colored and structured piece.  I'd be tempted to pry it open along one of the cracks and see what is inside.  I'm sure it is not fossil.

[Joeinmorgancounty]

2 hours ago, grandpa said:

Sure does look like some of the Keokuk Geodes I have in my collection from the Iowa/Illinois/Missouri Tri-State area.  I have some from that area that have similar coloration and botryoidal chalcedony structure.  I even think I see some gaps in the surface with dark crystals inside.  It's a beautifully colored and structured piece.  I'd be tempted to pry it open along one of the cracks and see what is inside.  I'm sure it is not fossil.

Thanks for checking this out. The stones really caught my eye, and are definitely paying a visit to the lapidary saw soon! I'll have to put a picture of a slab on here. Thanks again!