Cephalopod with a pleasant suprise

[minnbuckeye]

I have always enjoyed collecting cephalopods from SE Minnesota. My favorites are the ones providing a little extra!! Something that occurs quite often.  The example presented today was found a week ago. Didn't think much of it until I freed it from its matrix.  

 

 

 

 

The upper left was the part exposed. Not too impressive. I debated leaving it. Something told me to free this up and I am glad I did.

 

Here is the pleasant surprise:

 

 

!!. 

 

 

I assume the hollow nature of cephalopods create a perfect void for crystals to form in. correct me if I am wrong. I will clean the outer surface one day and it will end up being a keeper.

 

[jpc]

I think you are right.  We see this a lot in Cretaceous cephalopods.  Ammonite geodes.   

[Mediospirifer]

I've found some (small) horn coral geodes, and brachiopods. It may be a function of the original critter decaying to leave a void, which then fills with geode rather than solid. Or it could be a function of a critter with a harder outer surface; I don't know.

 

What I do know is that I like the crossover between the fossil collection and the mineral collection!

 

[Herb]

I see brachiopods as geodes and a few cephalopods.

[Ludwigia]

Minerals can fill any kind of cavity, including those existent in fossils, depending on the given geological conditions during formation to the present day. Minerals often fill the cavity completely, but when the formation process is interuppted before the cavity is completely filled, then crystals can be left on the walls. Calcite, which appears to be the case here, is found most commonly in fossils, since the mineral is derived directly from the shell substance and/or from the limestone which commonly provides the matrix in which the fossil is preserved.