The consensus is aluminum. Not sure where you found them but almost every spot where I have seen a campfire I have found similar. Some of the flaky balls are from foil and the solid ones are from cans. I can't say teenagers, but it's whomever go up there has a fire and they throw those items in the camp fire to dispose of them. Foil from things like sandwiches.....or home made paraphernalia. In other words it looks like only litter.