That's a neat rock. Certainly appears to have pyrite in it, but the discoloring on the last photo makes me think it could have bornite or chalcopyrite mixed in. Do you have a small enough chunk that you could see what color streak inside makes? Inside of the toilet tank works well. Pyrite is supposed to have a greenish-black streak.
I have a specimen right now that I'm trying to ID that has an extremely similar stucture to the inside of yours. However, its streak is distincly grey, and its specific gravity is markedly higher than pyrite. I reached out randomly to professors at Emory, UGA, and Georgia Tech and miraculously, all three are trying to help me ID it. The Ga Tech guy calls it a "head-scratcher." Anyway, take a look at this pic. Pretty close to yours.
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