I have pieces of what appears to be molten glass that I found on the shore in Marblehead Massachusetts that are similar to flint glass substances from Illinois.
All the pieces are small, under 150 grams, and appear oxidized (orange or brown) on the surface, yet black as the blackest obsidian inside, and unusually pure. The area is heavy with granite, which may indicate it is a form of granitic glass... but no nodules of such material appear in the granite formations, and the stuff is flawless as if it were a man made black silica.
They are a strange but not rare find, I can get some tomorrow if necessary. I also found micro quarts points on the same shore.