Jade

Jade is a mineral.

Source
Jade can be found in Gold Veins, Tin Veins and Iron Deposits everywhere. It is also a reward from the quest. It is also dropped from the elite mobs in Dun Modr. (As of patch 2.3, the elite tag has been removed from Dun Modr mobs.)

Prospecting Tin Ore (low chance) or Iron Ore can also yield Jade.

Jade as an ingredient
Jade is used in the following recipes:

Blacksmithing

 * Frost Tiger Blade
 * Golden Scale Cuirass
 * Green Iron Hauberk
 * Jade Serpentblade
 * The Shatterer

Engineering

 * Accurate Scope
 * Discombobulator Ray
 * Gnomish Battle Chicken
 * Gnomish Cloaking Device
 * Gnomish Shrink Ray
 * Green Lens

Jewelcrafting

 * Golden Dragon Ring
 * Jade Pendant of Blasting
 * The Jade Eye
 * Golden Ring of Power
 * Figurine - Jade Owl

Leatherworking

 * Gem-studded Leather Belt
 * Ironfeather Breastplate
 * Ironfeather Shoulders

Tailoring

 * Dreamweave Circlet

Jade as a quest objective
Jade is needed for the following quest: