Heart of the GuardianThe Heart of the Guardian is an ancient crystal that was rediscovered on the surface of Yavin IV by the Rodian inventor Suvam Tan some time prior to the Jedi Civil War. Possibly utilized as a lightsaber crystal by the redeemed Revan, it would have given the blade of any such weapon a unique bronze hue and yellow core. The Heart is one of two legendary crystals that Revan possibly obtained from Tan near the end of his quest to find and destroy the Star Forge, the other being the Mantle of the Force.
When placed within a lightsaber, it alters the properties of other crystals that the lightsaber carries in a positive way; this crystal creates a fast yet devastating blade that is perfect for lightsaber combat.
According to prophecies of the Jedi Order, the Heart would appear at the time of greatest turmoil and help in bringing the galaxy into to salvation. However, the Sith also believed it to be an object of their heritage, which in turn would have brought about their domination of known space.