Ghostfire crystal

When the crystals could be located, they could be used in the creation of lightsabers to produce a blade that was dim and translucent compared to the iridescent blades of other sabers, making it as difficult to detect as the crystals themselves. Lightsabers with ghostfire crystal cores also generated almost no sound and produced illusory afterimages of the blade that followed the motions of the wielder, the most curious effect of all which disguised the true position of the blade while also disorienting foes.

Ghostfire crystals were first mentioned in Endless Vigil, a supplement for the Star Wars: Force and Destiny roleplaying game written by Tim Huckelberry and James M. Spahn and released by Fantasy Flight Games in 2016.