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It's been more than ten years, but I've been thinking about a book I read as a kid. I can't remember any part of the title or author's name.
It begins with an old man who sits and ponders a stone in his hand constantly, which he's worn smooth. He takes on a boy or young man and teaches him the secret of magic by giving him progressively more physically difficult chores. The boy finally gets it when he's told to move an impossibly large boulder, but ends up yelling at it to move, which it does.
I remember that there were others who were taught magic, and the stone turns out to be some sort of magic orb, maybe a fallen star. These magicians are able to change into animals. It was a longer book, at least 700 pages. Hope someone can help...