Possibly they are not even solid objects at all but actually an electricity phenomenon. The Smithsonian even posts on their website please do not send them something you believe to be a meteorite, but to send pictures and they will contact you back. Just like buzz aldrin gifted a fake moon rock that turned out to be a piece of petrified wood, meteorites may be faked as well. Or another possibility maybe pieces of the Firmament itself but I don't think so personally.