The seemingly supernatural (to those not of their order) abililties of the Valar and the Maia can only be explained by the fact that they
are 'divine' beings, and as such have a power over the substance of Arda that allows them to do things that seem to transcend natural laws in ME. The ultimate source of that power could only be their Creator.
The powers they possess appear to be fairly generalized in that they don't seem to be limited to any particular expression. The Istari may be exceptions to this, however. Gandalf does make this interesting comment:
Quote:
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Radagast is, of course, a worthy Wizard, a master of shapes and changes of hue.
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FOTR The Council of Elrond
That would seem to say that each of the Istari might have a specialty of sorts. This is borne out by the fact that Gandalf's overt uses of his powers seem to mostly involve fire and explosions.
As for the Mirror of Galadriel, I have no idea how it works, or indeed who made it. But Galadriel was one of the Noldor, who made a few marvellous things in their time. Perhaps the Mirrior used some of the same arts as the Palantíri, as its workings appear to be somewhat similar: showing a concentrating viewer visions of persons and events past, present, and possibly the future.