Cephalopod or just chert concretion? #3

[Lauren16]

This is the 3rd post of features from a limetone/dolostone rock, found loose in a river, presumably carried south from the limestone bedrock further north. If this is just chert concretion, not a fossil, then Q How did the parallel grooves form?  The grooves in this feature had been emclosed in soft chalky dolostone material until I removed it with vinegar baths and much rubbing, so were not caused by weathering and are not glacial striae. 

 

And last, this is one of several bonelike features in this rock, that I understand are just chert, but the structure of the end looks bone-like to me. It was seeing these bone-like features sticking out of a normal limestone rock that caused me to soak the rock in several vinegar baths and keeping rubbing and brushing, which exposed all the small features with parallel grooves in this 3-post post.

 

[fifbrindacier]

With all the bath of vinegar you put that piece in, all shell have melted. If there is a fossil there it then must be an internal cast. I think this is limestone with probably infilled burrows.

[Lauren16]

Thank you for sharing your insights!

Lauren 

[Shamalama]

On 3/7/2020 at 4:33 PM, fifbrindacier said:

With all the bath of vinegar you put that piece in, all shell have melted. If there is a fossil there it then must be an internal cast. I think this is limestone with probably infilled burrows.

Agreed, might just be an infilled burrow or odd mineralization feature.