The Gem of Glory was a magical item that provided Vashtarr with his magical powers. Vashtarr accidentally used it to imbue Valerie Storm with similar powers to his own.

It gave both Vashtarr and Valerie Storm the ability to fire energy blasts from their eyes, as well as superhuman durability.

It gave Valerie Storm the ability to grow wings so that she could fly.

Vashtarr could also use it's power:

to fly
to create an army of Energy Constructs
as a viewing screen that could even see through time
as a form of limited Time Travel.
he also once turned to a red mist and hid inside the gem.

The Gem exploded when Valerie, Cinda, and Maya combined their power to destroy it. The explosion sent them into the past to the time and place that Vashtarr had abducted Valerie from.