Aquamarine

Aquamarine is a blue gem that ranges from the light blue of a winter sky to the deep blue of the ocean depths.

Source
Aquamarine can be mined from veins of Iron, Mithril, and Truesilver.

Prospecting Iron Ore (low chance) or Mithril Ore can also yield Aquamarine.

Aquamarine can also be found as a random world drop from creatures of level 25+ in Kalimdor and the Eastern Kingdoms.

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

Blacksmithing

 * Blue Glittering Axe
 * Dazzling Mithril Rapier
 * Heavy Mithril Helm
 * Ornate Mithril Boots
 * Phantom Blade
 * Truesilver Gauntlets

Engineering

 * Catseye Ultra Goggles
 * Deadly Scope
 * Gnomish Harm Prevention Belt
 * Green Lens
 * Ultrasafe Transporter: Gadgetzan

Enchanting

 * Enchant Boots - Minor Speed

Jewelcrafting

 * Aquamarine Pendant of the Warrior
 * Aquamarine Signet
 * Figurine - Truesilver Crab
 * Gem Studded Band
 * The Aquamarine Ward