Secret of the Crystal (Time Travel Adventure) by Brian K. Larson
Jhahnahkan has returned to Ackturra from the outer rim on a mission to find allies in their failing war with the Zelinites.
He has been given a seat on the High Council, and issued a power crystal from the Ackturrian caverns. These crystals, give the user special abilities. But, something about the crystals he mistrusts. Jhan is plunged one-thousand years into the past.
Now, he must discover the secret of the crystal before his brother takes over the council and commits genocide.