This lore is found on Ilum.
To the Jedi, Ilum is a sacred world invaded and ravaged. To the Empire, it represents vital resources and the chance for a powerful symbolic victory. After learning of the value of Ilum’s crystals in the years after the Sacking of Coruscant, the Empire sent a small group of Sith to investigate the planet. With only a handful of Jedi scattered across the ice plains, the Sith were able to avoid or defeat their foes and begin quietly harvesting Ilum’s crystals. During the fighting on Corellia, Republic SIS operatives recovered evidence of the Empire’s plans to use these crystals and develop stealth technology on an unprecedented scale. The Republic gathered its fleets and allies–both old and new–and raced in defense of Ilum. The aid of the Jedi has allowed the Republic to establish strong bases, but the Empire is determined not to lose such a valuable world. The battle for Ilum promises to be long and bloody.