Arcanite Bar

An Arcanite Bar is a rare metal used in many level 60 recipes. Not only is it a component to making many items, but it is also needed to create Enchanted Elementium.

Source
This item is created by Alchemists using the Transmute: Arcanite ability which requires a skill level of 275 and a Philosopher's Stone. The recipe can be learned from Alchemist Pestlezugg in Gadgetzan. Transmuting Arcanite won't trigger shared 20-hour-transmute cooldown.

Blacksmithing

 * Annihilator
 * Arcanite Champion
 * Arcanite Reaper
 * Arcanite Skeleton Key
 * Black Amnesty
 * Blackfury
 * Blackguard
 * Corruption (sword)
 * Dawnbringer Shoulders
 * Ebon Hand
 * Enchanted Thorium Breastplate
 * Enchanted Thorium Helm
 * Enchanted Thorium Leggings
 * Frostguard
 * Gloves of the Dawn
 * Hammer of the Titans
 * Heartseeker
 * Heavy Timbermaw Boots
 * Icebane Bracers
 * Icebane Breastplate
 * Icebane Gauntlets
 * Ironvine Breastplate
 * Invulnerable Mail
 * Lionheart Helm
 * Nightfall (axe)
 * Persuader
 * Runic Breastplate
 * Runic Plate Boots
 * Runic Plate Helm
 * Runic Plate Leggings
 * Runic Plate Shoulders
 * Sageblade
 * Serenity (mace)
 * Stronghold Gauntlets
 * Sulfuron Hammer (used to create Sulfuras, Hand of Ragnaros)
 * Titanic Leggings

Engineering

 * Core Marksman Rifle
 * Delicate Arcanite Converter, used to make:
 * Arcane Bomb
 * Arcanite Dragonling
 * Biznicks 247x128 Accurascope
 * Bloodvine Goggles
 * Bloodvine Lens
 * Voice Amplification Modulator
 * Zapthrottle Mote Extractor
 * Flawless Arcanite Rifle
 * Force Reactive Disk

Jewelcrafting

 * Emerald Crown of Destruction
 * Figurine - Black Diamond Crab
 * Figurine - Dark Iron Scorpid
 * Figurine - Emerald Owl
 * Necklace of the Diamond Tower

Tailoring

 * Cloak of Warding

Mining

 * Smelt Enchanted Elementium (used to create Thunderfury, Blessed Blade of the Windseeker)

Jewelcrafting

 * Necklace of the Diamond Tower

As a quest objective

 * Arcanite
 * Collection of Goods
 * A Gesture of Commitment
 * The Good News and The Bad News
 * Breastplate of Bloodthirst
 * Leggings of Arcana

The Tier 3 armor quests at Light's Hope Chapel in the Eastern Plaguelands (Only available after completing Echoes of War.) Please note that the following have been removed from game as of patch 3.0.2.

The frost resistance armor quests at Light's Hope Chapel in Eastern Plaguelands (Only available after completing Echoes of War.)
 * Icebane Bracers
 * Icebane Breastplate
 * Icebane Gauntlets
 * Ramaladni's Icy Grasp

In the RPG
This grayish metal looks dull even when tempered, but it holds a keener edge than any other metal on Azeroth. Arcanite is extremely flexible and can be worked into a springy armor that turns aside the mightiest blows. Only weapons, armor, and shields normally made of metal can be fashioned from arcanite; a warblade can be made of arcanite, but a tauren totem cannot.