Impact
The impact crystals, a duo of yellow lightsaber crystals, belonged to a clone derived from Galen Marek. These crystals enhanced the clone's lightsaber attacks, enabling him to inflict greater harm. Their slight pulsation indicated that they were compressed energy crystals.
Behind the scenes
Specifically, these lightsaber crystals were only available in the Collector's Edition of the video game Star Wars: The Force Unleashed II.