Hot glass?

I’ve been digging in my yard and I somewhat frequently get high signals (35-40 on the Eqinox) at various depths. When I dig them I get... hot glass? Fairly large chunks of blackish, greenish, blueish irregular obsidian-looking glass that drive the detector wild. The signals are clear, repeating, and solid. My pinpointed picks them right up with full accuracy. I find them in all metal, Park 1 and 2, and Field 1 and 2. They’re not magnetic and have no overt metallic characteristics besides being detected by the Equinox. I know it’s not anything “special” besides looking kind of cool, but does anyone have any information on what these things are or their possible origins? I’ve asked a few rock hounds and their guesses don’t match what I’m finding. The picture is of two of the larger examples, but I’ve found smaller smooth ones with almost polished round shapes.