Meditation crystal
A meditation crystal on Tython Crystals of meditation were naturally formed rocks that aided in the practice of meditation. These crystals grew naturally on the Deep Core planet of Tython. Small pieces of a meditation crystal could be inserted into the hilt of a lightsaber. This would generate a focused energy beam and help the user maintain a stronger connection to the Force during combat. This stronger connection helped the user conserve energy instead of losing it during fights.
Rahm Kota, a Jedi Master, gifted two of these crystals to a clone of Galen Marek, a former Sith apprentice, while en route to the Salvation.
Behind the scenes
In The Force Unleashed II, Marek uses these crystals for most of his journey. They allowed him to regenerate Force energy each time he landed a blow on an enemy.
Although Marek is shown with two of these crystals in cutscenes as early as Dagobah, it's impossible to get more than one in the game before reaching the Salvation. However, the novel states that the crystals are only blue during his vision on Dagobah, and he still wielded red-bladed weapons at that time. In the novel, he received the Meditation crystals on the way to the Salvation, but in the game, he gets the second crystal about halfway through the Salvation.