[Source] A Massassi piece was a type of crystal that was an artifact of the ancient Ordu Aspectu, a splinter group of the Jedi Order. Associated with the extinct Massassi species, Massassi pieces were used as activation keys at the Great Temple at the Massassi Site on the moon Yavin 4, and at the space station-fortress base of the Ordu Aspectu, the Citadel of Rur.