Clamlike fossil / petrification

[gino22]

This was a garage sale find amongst a lot of interesting items. Many have offered clam fossil as a guess, but the texture and unusual density have me curious.

Examples of fossilized clams online are quite a bit more obviously clam shaped. There is a clean groove down the middle that accommodates a finger nicely. So maybe some kind of primitive striking tool?

Here are pics. I know next to nothing about this kind of thing, so could be a simple clam for all I know:

 

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[gino22]

 

[gino22]

 

[gino22]

 

[gino22]

Sorry for the multiple posts, my phone crashes when trying to insert multiple images

 

[austin]

pelecypod, bivalve fossil, cretaceous era, 60,000,000 plus years old, generally found in limestone here in Texas, but mineral replacement happens like in yours perhaps...

 

[Inyo]

Deleted by author.

 

[gino22]

On the money, thanks so much for the quick and thorough responses.