Kyber Dragonshard

Khyber dragonshards are generally a dark blue or black and can be found beneath the surface of Eberron in deep underground caverns. While Siberys dragonshards are the hardest to find, Khyber dragonshards are the most dangerous to obtain because of the denizens lurking in Khyber. Khyber dragonshards have an affinity for binding and are most notable for their use in crafting bound-elemental items, such as the lightning rail.
Marcella and The Dragon Syndicate reclaimed the Eston Forge of Creation - Mournland and seems to be able to now be able to produce this incredibly rare resource.