The Magic stone mine is a special mine that can be accessed during the quest Tears of Guthix. It is located in the Tears of Guthix cavern. This mine is the only place where Magic stones can be mined. Talk to Juna and she will tell you about the story of the light creatures. You must have started Tears of Guthix and have a sapphire lantern with you to access the stones. After the quest, the mine is still accessible, and Larger rock can be mined to create Ornate bowl.
As in the quest, the mine is accessed by going to the point northwest of Juna where light creatures come to the edge of the chasm, and using the sapphire lantern on one of them.