Weird Kentucky Cave Fossil

[Rockwood]

5 hours ago, FossilNerd said:

I try to remember that once upon a time, the norm was to think the world was flat

Yea. 2020 was a strange time. 

[CaversFossils]

So, someone on Facebook identified it for me. He gave his credentials and he seems knowledgeable, so this will be what I believe until proven otherwise!

 

"It is a large fragment of a dorsal spine from a large cartilaginous fish. I have seen them up to 18 inches long in the Salem Formation in Missouri"

[Harry Pristis]

My reaction to the images is Family Pinnidae, cf. Atrina sp. -- a pen shell.

[CaversFossils]

Ok, update: a guy with real mammoth cave fossil ID creds just told me that he believes it's a shark brain case. I'll update you guys later because he only sent me a quick email about it. But I'll talk with one of the guys at mammoth tomorrow.

[hemipristis]

On 12/31/2020 at 12:17 PM, CaversFossils said:

We didn't have a UV light on hand. 

 

Also, ill add that I've never heard of vivianite, so that's interesting.

I’m aware of Vivianite-replaced fossils from the  from the Ukraine (bivalves), and the NJ and MD Cretaceous. To form such usually requires a substantial source of phosphate, such as from bones and teeth. It’s presence (if that’s what it is) in Mississippian limestone is unexpected,

. The mineral is also usually a darker shade, think ‘midnight blue’

 

 

[Mahnmut]

6 hours ago, hemipristis said:

I’m aware of Vivianite-replaced fossils from the  from the Ukraine (bivalves), and the NJ and MD Cretaceous. To form such usually requires a substantial source of phosphate, such as from bones and teeth. It’s presence (if that’s what it is) in Mississippian limestone is unexpected,

. The mineral is also usually a darker shade, think ‘midnight blue’

 

 

Never thought about the phosphate in mollusc fossils.

I have seen very different amounts of vivianite in bone or tooth fossils, where iron replaced some of the calcium of the apatite that made up the original substance. There might be only a slight greenish tint, there is a bright blue variant called "bone turquoise" that I would love to have in my collection. And there are the midnight blue pieces you mentioned. It depends on the amount of replacing iron and may also darken with exposure to oxygen and light. Even pure crystals of vivianite are often colorless when fresh from the mine, turning darker fast.

I also had the luck to acquire one of the molluscs from Kerch in the late nineties, it was midnight blue then and among the proud of my collection. Sadly turned midnight black after some years. I never thought about where the phosphorus came from in the mollusc shells (soft tissue aside).

Best Regards,

J