I'm guessing some sort of slag or "klinker". Refuse from sort of forging operation or a coal "klinker".
Coupla years ago I snagged a few rock looking things out of our chain of lakes that looked similar to that only smaller. Couldn't get anyone to tell me what they were. They were pretty heavy until they dried out, kinda porous, broke apart fairly easily. In reading a history of the area the first postal service had a coal fired steamer they ran the chain with to deliver mail. The light came on. Same route every (or most every) day, probably pretty predictable dumping klinkers so they could stoke the boiler.
Looking at it again it does look "metalish" and seemingly rusty. Despite being non-magnetic ( which pretty much rules out a meteorite) is probably some sort of slag that was dumped or skimmed off of some forgery operation. Be interesting to know where it came from and how it got to where you found it.
Let us know if you ever find out for sure...
