Katak
Not much information existed regarding Katak Crystals or where they came from. These crystals were typically only discovered inside the lightsabers wielded by dark side adherents to the Force. Those who utilized lightsabers containing this crystal could leech a bit of the life energy from individuals nearby. While this wouldn't immediately exhaust the target, extended periods of exposure could lead to death.
Behind the scenes
Within the game Star Wars: The Force Unleashed, obtaining the Jedi holocron located above the tallest turbolaser beam on the partially constructed Death Star unlocks this particular crystal. When a lightsaber is equipped with this crystal, certain attacks enable the player to absorb a fraction of their opponent's health.