The Root of all Evil.

[drigel]

I am going to lift some quotes here. They are from a Martinez essay (Magic by Melkor, No Returns Accepted), where he used quotes from "Notes on motives in the Silmarillion":

"...Morgoth's power was disseminated throughout Gold, if nowhere absolute (for he did not create Gold) it was nowhere absent. (It was this Morgoth-element in matter, indeed, which was a prerequisite for such 'magic' and other evils as Sauron practised with it and upon it.)"

and

It is quite possible, of course, that certain 'elements' of conditions of matter had attracted Morgoth's special attention (mainly, unless in the remote past, for reasons of his own plans). For example, all gold (in Middle-earth) seems to have had a specially 'evil' trend -- but not silver. Water is represented as being almost entirely free of Morgoth. (This, of course, does not mean that any particular sea, stream, river, well, or even vessel of water could not be poisoned or defiled -- as all things could.)

I am also leaning toward Martinez theory concerning mithril. Possibly what made mithril so special was the absence of the Morgoth element.