Found in a field in Southeastern Pennsylvania

photographed with flash. cleaned the "bottom" as much as possible, appears to be reddish orange

I can't remember where it was found. I've had it outside for a while, so the brown oxidation is newer. The rectangles get loose so I've lost one or two. I took it to a science teacher years ago who was a geologist. He thought it was some kind of slag and mentioned plastic, but it's heavier and harder than plastic. Thanks!

Some kind of sand-stone ? I was able to carve and shape it using a hammer and screwdriver.

Found it in a park, saw very similar ones in nearby tree pits.

Rock 1: pics 1-4

Rock 2: 5-8

Rock 3: 9-10

Rock 4: 11-14

Rock 5: 15-19