There was once a powerful sorceress who plotted and schemed for power. When those plans fell through she engaged her former teacher in a magic duel. A duel which resulted in her being locked in a vein of quartz crystal.
For many years afterward the cave in which the sorceress was imprisoned became a place avoided by the superstitious locals. And over time the stories slipped into fairy tales told by parents to get their children to behave lest they be cursed by the “witch in the rock”.
And thus for fifteen hundred years she slumbered. And waited for the eventuality that someday, someone would come along and set her free.