This author knew the sectioned slab pictured below could not be iron-furnace slag, and jumped to the conclusion that this material was the chemically-reduced igneous crust of a hot-classical Kuiper belt object that impacted Earth as the YD-impact comet on the Laurentide ice sheet, 12,800 years ago, and was delivered to Central Pennsylvania, embedded in a ballistic ice-sheet fragment.  Instead, this author now understands the pictured material is merely industrial lead-silver slag, where the metallic-iron inclusions are merely a waste product of the lead-silver smelting process.

Sectioned slab of presumed industrial lead-silver slag, containing metallic-iron inclusions