Large Opal

Large Opal is a raw gem.

Source
This item can be mined from Small and Rich Thorium Veins or prospected from Mithril Ore and Thorium Ore. It can also drop from high level mobs in Eastern Kingdoms and Kalimdor.

As an ingredient
Large Opal is used in the following recipes:

Blacksmithing

 * Arcanite Champion
 * Darksoul Breastplate
 * Darksoul Leggings
 * Darksoul Shoulders
 * Enchanted Thorium Helm
 * Heartseeker
 * Helm of the Great Chief
 * Masterwork Stormhammer
 * Ornate Thorium Handaxe
 * Serenity (mace)
 * Stronghold Gauntlets

Engineering

 * Dark Iron Rifle
 * Ultra-Flash Shadow Reflector
 * Voice Amplification Modulator

Jewelcrafting

 * Opal Necklace of Impact
 * Simple Opal Ring
 * Emerald Crown of Destruction