Lumenstone

Lumenstone is described as being "an enchanted material that can negate magic, even withstand great amounts of fel." It is located in rare amounts all over the Broken Isles and used by the native races in metalcrafting. It is used to craft both weaponry and armour.

Both the Highlord and High Priest — adventurers — sent out their champions from their respective Class Halls to collect lumenstone as part of their preparations against the Burning Legion's upcoming assault on Netherlight Temple.

Source
This item is obtained by completing the following Class Hall missions:


 * Lumenstone: Broken Shore
 * Lumenstone: Faronaar
 * Lumenstone: Stormheim
 * Lumenstone: Suramar City
 * Lumenstone: Val'sharah
 * Lumenstone: Vashj'ir

As a quest objective

 * Lumenstone (paladin)
 * Lumenstone (priest)