What Boo is refering to is a thread around here somewhere entitled "The Pendant and the Telepod" or something like that in which this question was addressed in depth. I may well be remembering wrong, but every scrap of information we could find about the pendant and the telepod were covered extensively. The basic conclusion that the thread came to was that the pendant was most likely responsible, and not in an inanimate object sort of way either. We see throughout the game that the Pendant has a semblance of intelligence, so it choose to essentially start everything.
Of course, just because we discussed it before doesn't mean anything; new ideas can topple established theory.
So, then, what was the telepod made of? No one knows. Dreamstone could be in there, but probably not as that would make Lucca's reaction to processing the dreamstone odd. Since the gates seem to be energy based, and the Telepod functions along seemingly similar lines (transporting between locations in the 3rd dimension is fundamentally similar to transporting in the 4th), I'd go with the appearance of the gate being an energy reaction, not a reaction of dreamstone to... something. Admittedly, the gatekey is a convenient plot device and there is no realistic way Lucca could have developed it, it is a game and she is a genius.
