The Great crystal functioned as a dark side artifact, acting as a prison for the spirits of numerous Jedi Masters. These spirits were confined within the Great Temple situated on Korriban.
This enormous crystal, violet in color and pulsating with energy, was housed inside the Great Temple located on Korriban. It held the spirits of Jedi Masters who had succumbed to the power of the ancient Sith. After the Sith deserted Korriban, the crystal and its captive souls were forgotten, resulting in an unending torment for the imprisoned Jedi.
During his efforts to lure Jedi Padawan Exar Kun to the dark side of the Force, the spirit of Sith Lord Freedon Nadd led him to the crystal. This served as the ultimate test of Kun's dedication to the Sith path. After Kun expressed his thoughts on the terrible predicament of the Jedi Masters trapped within, Nadd resolved to "free" both the spirits and Kun from the influence of the light side. Nadd shattered the crystal, obliterating the Jedi spirits it contained and triggering a landslide that almost resulted in Exar Kun's death.