My son (12yo) rockhounds while I fish. He mainly collects for color. He does his best to identify them, he likes to label and display them in his room. He found 2 that we have had no luck identifying. They were found on a gravel bar on the Schuykill River in Philadelphia, PA. The larger one has a glassy, white coating with a hard sandy looking bluish gray interior. Not sure if this is natural or construction debris. The small ones are almost perfectly spherical, they look like they've been tumbled in the river for quite some time. Almost completely black. When broken open they look like charcoal inside, but much harder. Any help would be greatly appreciated.

Hmm this is potentially from the Pottsville Formation -- Gray conglomerate, fine- to coarse-grained sandstone, and siltstone and shale containing minable anthracite coals.

https://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=PAPAp%3B7