Guardian of Atlantis - Raven Weir Chronicles, #1

Raven Weir isn't who she thinks she is. On her sixteenth birthday, Raven receives a mysterious necklace, that is the key to a power hidden for centuries in Atlantis. With the help of her new best friends, Raven must learn to control her growing powers and keep the necklace out of the hands of those who would use the power to rule the world. Can Raven survive as the Guardian?