This is a children's book containing seven chapters. It is a mystery novel for young readers, and is the second book in the Clue Duo series. The book follows the story of a girl named Elisabeth VanKlewen and her best friend Eveline Brighton. Both girls share a desire to solve mysteries, and it is in this book that they get their second opportunity to do so, as they solve the case of the missing mineral. As the mystery progresses, the girls learn that sometimes, the answer to a case can become crystal clear. A rock solid piece of reading for young readers.