I doubt that Tolkien had a real metal in mind. He said of lembas that no
chemical analysis would have revealed the secret of its magic, and I suggest
the same is true of
mithril.
“I dislike Allegory - the conscious and intentional allegory - yet any attempt to explain the purport of myth or fairytale must use allegorical language. (And, of course, the more 'life' a story has the more readily will it be susceptible of allegorical interpretations: while the better a deliberate allegory is made the more nearly will it be acceptable just as a story.)” (From Tolkien Letter # 131.)
