Blue John

The Queen of Darkness lives under the ground in the shadow of a mountain, Mam Tor. Before she was carried down into the shelter of the cavern, she snatched the two things she could not bear to leave behind - the purple-blue heart of the glacier and the gold of the sun. Out of these she makes a child and names him Blue John. He lives in the caves with her, forbidden to go out into the light. One day a party of children comes to the caves and Blue John follows them out into the sunshine and is turned to stone. (Blue John is a precious stone mined in the Blue John and Treak caverns of Derbyshire. The name is said to come from the French bleu-jaune.)