Crystals are items that can be used against the Grocks. You acquire Crystals buying with the Mayor's village or dropped after defeating Grocks (in field). These Items allowsgivesrocks. There is a total of 7 different types of crystals.
Crystal Shield: The crystal "Shield" that can only be used on the Train and the Cart. It protects the vehicle for a short period of time from attacking grocks. This crystal is only available in The Last Ranger.