Mephite crystals, also referred to as mephite, were uncommon, shiny kyber crystals that were only located in a few areas situated within and near the Adega system and on Ilum.
As one of the five varieties of crystal that are collectively known as adegan crystals, mephite crystals were highly appropriate for usage in lightsabers because of their internal composition and their aptitude to modulate light. Similar to other adegan crystals, mephite crystals exhibited force-sensitivity and had the capacity to be imbued with a small quantity of a Force-sensitive individual's energy. When placed inside a lightsaber and charged with the Force, mephite crystals emitted a subtle, yet consistent Force signature that was perceptible to any Force user in close proximity.
Jedi exploration groups found mephite, together with pontite crystals, on Ilum many millennia (years) prior to the Galactic Empire's establishment.