Azerothian Diamond

Azerothian diamonds are eternal.

Source
Azerothian Diamond is a rare mineral mined from Thorium Veins and Obsidian Chunks. They can also be found in Solid Chests, and obtained using prospecting.

As an ingredient
Azerothian Diamond is used in the following recipes:

Blacksmithing

 * Arcanite Champion
 * Blazing Rapier
 * Bloodvine Lens
 * Ebon Hand
 * Enchanted Thorium Breastplate
 * Enchanted Thorium Helm
 * Frostguard
 * Heartseeker
 * Invulnerable Mail
 * Lionheart Helm
 * Obsidian Mail Tunic
 * Whitesoul Helm

Engineering

 * Flawless Arcanite Rifle
 * Hyper-Radiant Flame Reflector
 * Ultra-Flash Shadow Reflector

Jewelcrafting

 * Diamond Focus Ring
 * Figurine - Black Diamond Crab
 * Glowing Thorium Band
 * Necklace of the Diamond Tower

Tailoring

 * Mooncloth Circlet

As a quest objective

 * The Divination Scryer
 * True Masters of the Light (2)
 * Material Assistance
 * The Good News and The Bad News