Kyber Crystals

Kyber crystals (Usually known as Lightsaber Crystals) are used to customize your lightsaber blade's color. Once you have found one, it will reward you EXP, and another customization option for your lightsaber upon discovery. There are currently 10 Kyber Crystals in game with 3 different variants: Normal, Unstable, and Dark Core. That changes the way the color looks like on your Lightsaber. Normal colors are just that, clean sleek and ordinary, unstable crystals reflect the cracked crystal of a Sith's lightsaber, which in the lore of the Star Wars Universe is said to make the Lightsaber stronger, and Darkcore Crystals change the color to reflect the look of the Dark Saber, although still tinged with the Crystal’s color.

You can find a complete guide to finding every single Kyber / Lightsaber Crystal right here:

Lightsaber Crystals

honestly, we don't even need this page since the Lightsaber Crystal page already describes this AND gives the location information