- As of Patch 1.9.0
Epic items that are level 51 and above will now 
[Disenchant] into a Nexus Crystal. Also items that normally disenchant into Large Brilliant Shards have a very small chance of disenchanting into a Nexus Crystal. New more powerful enchanting recipes that require these crystals can be found in the new Ahn'Qiraj content.
The crystals will be possibly be useable in Jewelcrafting (Burning Crusade) and in high-end Enchanting recipes found in Ahn'Qiraj.