🔎 UNIDENTIFIED Copper or Brass? And What Iz It?

[USNFLYR]

Found this near a Pensacola bayou shoreline. We a have found many square nails, Spanish pottery shards and round balls in the same area. It was found where fresh water (spring?) flows into the brackish water. I suspect, in the early 1800's, it was a source of fresh water replenishment. It was near an early British plantation. I’ll attach both "before and after" photos. This very heavy, solid item seems to have been broken at a right angle….and there appears to be cross hatching markings that was crimped into the side in order to make an attempt at adding an ornate design.

Question: It appears green after I wash it, yet I can see a brass patina underneath…but how do I know if this is a brass or copper piece?

And, can anyone take a stab at what it is? Nautical? Horse/farm accouterment?