Crystals

Crystals are special items dropped by Monsters, like potions and gils. They aren't dropped as often though. Crystals are used for various tasks, like combining items together or "growing them." There are 8 types of Crystals, each representing the 8 elements of Vana'diel. The main way to receive Crystals is to fight monsters with your own level or a little higher. They made it like this so you, who might be at level 20, won't go off to a lower level zone and just stock up on Crystals from the tiny little critters. You start out by walking over to a border guard from within a zone which your country controls, and ask him to cast the spell "Crysta." Crysta lasts for a limited time only. Once he/she casts it, you can start smacking up all the monsters you can and try to receive some Crystals. There is no guarantee that each monster you defeat will drop one. Remember to kill the harder monsters to have more of a chance to get some Crystals

The Fire Crystal is used for burning or heating an object.
The Water Crystal is used to liquefy (melt) objects.
The Ice Crystal freezes items making them hard.
The Earth Crystal is used to combine or connect items together.
The Wind Crystals is used to cut and divide objects.
The Thunder Crystal is just like Wind only you are using it to finely cut an object to use with the Earth Crystal.
The Light Crystal is used to enrich an item.
The Dark Crystal is used to Corrupt or Decompose the item.