Flare - The Sunless World, #3

The mages of old saved their world, but left it in eternal darkness. Now it's time to bring back the light. After two years of training his magical gifts, Rafe returns home to a land wracked by war. Desperate states struggle to protect their resources of luminous quartz. Magic pulses and earthquakes devastate a world on the brink of extinction. Rafe's old enemy Karzov has gathered a band of prodigies obedient to his will.
He seeks the power of the ancient mages for an audacious and sinister purpose. It's up to Rafe and his ally, Isabella, to stop him-and undo the mistakes of the past to put their world right again.