As for this one,I also like how it looks xD and it was pretty cool in the anime.Also as it is strong to earth and water (and wood I think) it is useful especially for us who don't have all elements because we can replace some basic ones with it.
Basically it allows the user to either manipulate existing crystals or convert solid matter or some liquids into crystal,which includes earth and water techniques and use it in various ways,both offensively and defensively.It can't crystallize energy based elements so it is weak to fire and lightning,sound also.