It would really help if people gave the location where they found their specimens. It looks glassy enough to be obsidian but there are large swathes of the country where obsidian does not occur and then slag is the more likely possibility. In general, obsidian is not found in the Eastern United States… often expressed as “doesn’t occur naturally east of the Mississippi River”, although that's not 100% true as a statement.
If you can see bubbles, that's also an indication for glass slag rather than obsidian.