Example of how they are formed
One peaceful day, a little fish was swimming in the ocean. The fish's predator is a Great White Shark. The fish had no idea what was coming to him. The fish had been careful all his life to not be eaten by the shark. The shark was being very sneaky to eat his lunch. The shark got closer and closer. Then, the shark made his move and gobbled the fish. The shark did not like the bones and spit the bones out. After many years the bone got covered by sand and rocks. The minerals take over the bones and harden it. Very soon the bone becomes like rock.