So I guess the question is, then, when Thor sets the hammer down, why doesn’t it punch a hole in things due to gravity working on its intense mass? I can accept Thor being able to lift the hammer (after all, he has a magical bond with it), but when he’s not touching it… I mean, remember that scene when the hammer was pinning Loki to the bridge? Why didn’t it go straight through his chest? Remember when it landed in a field when Thor fell out of the helicarrier? Why didn’t it end up in a deep pit? Potentially, gravity on Asgard could be quite different, but there’s got to be something awfully magical about the hammer to keep it from following the laws of physics in Midgard.
And that doesn’t even bring up Mjolnir’s handle (haft?) and strap (leather thong? bit of rope?). What in the nine realms is it made of?
Basically it doesn’t matter what Mjolnir is made of. It’s a symbol. It’s made of something rare and difficult to obtain [not of this world] and beautiful and hard. It could just as well be made of, oh, the bones of mythological creatures. Or something.
File these questions next to “Does Bruce Banner weigh 1000 lbs or does the Hulk weigh 160?”