While digging even further underground, the drill bit on the Drill Engine Train breaks. The Pteranodon Family find themselves in the Cave of Giant Crystals, where they learn all about rocks and crystals (what they are, how they're different, how they form). In order to get back home, the Pteranodon Family has to fix the drill bit by finding a mineral harder than the mineral that broke the bit in the first place. Story B Educational Objectives: Minerals form naturally in the Earth and are made of the same thing all the way through, while rocks are made up of a bunch of different kinds of minerals. Minerals come in thousands of different types (more than 4000 to be more exact), many of which form large and beautiful crystals, some of which are harder than others.