45 year old mystery

[diginupbones]

 My dad found this on a construction site over 45 years ago and it got stuck in a drawer and never identified. We used to jokingly call it the caveman finger but I’m sure it’s just some sort of geological formation. Any clues? 

 

[Archie]

Cool piece, concretion coated with pyrite maybe?

[Mark Kmiecik]

+1 concretion.

[abyssunder]

I suppose, we will never find out what the core of it might be.

[diginupbones]

I’ve got no problem with cutting it in half! 

[diginupbones]

Finally took a hammer to this thing, does anybody know what kind of mineral/rock this is?

[FossilNerd]

Looks like pyrite to me. 

[Mark Kmiecik]

+1 pyrite. Probably solid end to end. The silvery part where you broke it will eventually oxidize and turn the same color as the outer surface.

[diginupbones]

Thanks! I just googled pyrite and that makes sense now because when I smacked it with a hammer and chisel sparks flew and it smelled like gunpowder. 

[Mark Kmiecik]

11 minutes ago, diginupbones said:

Thanks! I just googled pyrite and that makes sense now because when I smacked it with a hammer and chisel sparks flew and it smelled like gunpowder. 

Very good observation. That nails the ID down. You can try coating it with clear acrylic to preserve the shine but it may not work. Pyrite is finicky that way. Google "pyrite disease" and you will probably find half a dozen proposed solutions, of which one or two may work. Sometimes the substance you use in trying to preserve it will actually react with the pyrite or act as a slow catalyst in the process.