It’s got a bumpy surface not smooth, I found on a creek bed shared with mussels that grew to about 4 inch size… I thought it was coal, then I relalized it was a rock but wasn’t heavy at all which is strange
Looks like Magnetite but you should do a streak test on unglazed white (and black if you can) porcelain and a quick hardness test (fingernail, iron, quartz, etc ),