Ok, I guess I'll write about my one and only series.
The fist book is about a girl named Thaea (Th-A-a) and a boy named Feren. They are both in their late teens and are walking through a forest in England when they come across a a giant diamond (or Heaven's Gem as it's known later). The diamond is split into four parts: red, blue, white, and green. Feren touches the red part and becomes immortal and has the power to conjure and manipulate fire. Thaea then touches the blue part and has the power of water.

What they didn't understand then was that touching the magical gem also brings out and strengthens your desires and personality. Feren became evil and Thaea good (although they were both good to begin with, Feren was angry when he touched the gem). From there they have many adventures and more "Element Workers" are created.
In the second and third books (maybe fourth) the descendants of the first "Element Workers" are brought together to form a school (I.M.T.Y Institute for Magically Talented Youth). The main characters are:
Jessica 16 (one of the last with the power of water and the newest member of the school)
Alex 18 (the wild and athletic girl with the power of wind that, nobody really knows about)
Collin 17 (the powerful fire wielder and subsequently Jessica's crush)
Sam 12 (the small kid always getting in trouble, but surprisingly strong with his power of earth).
It's kind or complicated but that's the general idea. Hope you like it!

Dragon for fire
Dolphin for water
Unicorn for wind
Lizard for earth