The Korybite crystal was a very rough Korribani lightsaber crystal. Due to its rarity, it was seldom found in use and, if so, it was mostly hidden in a lightsaber hilt. Korybite gave lightsabers a black blade with a bright red glow, as opposed to the normal, white blade.
Korybite was the crystal used in Darth Vicious' lightsaber, the Blade of Abyss. Previously, Korybite had also been used as a gemstone. It was said to increase one's concentration via the Force.