Ghostfire crystal/Legends

Ghostfire crystals were a lightsaber crystal found on various Outer Rim planets.

Description
Only harvested from a very particular rock formation found on a handful of planets, the ghostfire formations were precarious spires of transparent stones typically found on mountain peaks. When harvested an inserted into a lightsaber hilt, the crystal produced a near translucent blade, that shone dimly and left an illusory afterimage. Aside from their lack of color, the blade was made more unique in that it did not resonate with the legendary thrum of most lightsabers; instead it was nearly completely silent.