A lightsaber crystal was one of a variety of crystals, gems, stones, or other objects used as the focus of a lightsaber.
At the heart of every lightsaber was a set of crystals that resonated to produce the efficient, powerful blade. While the most common crystals used in the process were from the Adegasystem, Ilum, and Dantooine (in the so-called Crystal Cave), Jedi and Sith used a variety of crystals to produce various colors, effects and unique abilities. Some crystals could even enhance the Force skills of a particular user. Other gems, such as colored crystals or diamonds, were used exclusively for prismatic effects. However, not all lightsaber crystals were actually crystals. Plenty of Jedi or Sith used a different material or substance in place of a crystal, such as physical remains, shards of glass, and even special micro machinery.
During the Great Sith War epoch, many lightsabers were created using Kunda stones, a natural geologic formation from the planet Kadril, in place of crystals. These stones boasted numerous practical applications in medicine and communications; however, when added to other focusing crystals, they produced a broader beam.