Mystery find from the gulf

[Kieth-Tx]

This was in a calcification the size of a bowling ball. Had been soaking it in muratic acid for 5 hours till I could see what was in it then I chipped away the rest. It still has a little bit on it but it weighs just over 7 1/2 pds. Any ideas?

 

[GKMan]

The pics are a bit small to see much detail... Is that a groove in one side of it?

 

[Kieth-Tx]

It is flat on two sides and the other two the sides curve in about an inch.

 

[GKMan]

I was thinking something for creating a looped end in a cable. My father had antique steel cables and I thought they had something like that where the cables laid in those grooves.

 

[Kieth-Tx]

Have found no markings on it but in cleaning it a small piece broke off....it is solid cast iron.